You have a company abroad and work to do in France. Instead of hiring a French employee, you send one of your own people: an engineer for a three-month installation, a consultant for a launch, a team for a harvest or a building site. French law has a name for this, secondment (détachement), and a full enforcement machine behind it: a prior declaration on the SIPSI portal, a representative on French soil, translated documents available on demand, minimum-wage and working-time rules from day one, and fines of up to 4,000 euros per worker that can freeze your project. Get it right and secondment is the most flexible way to start operating in France; get it wrong and both you and your French client can be ordered to pay. This guide explains the three lawful posting routes, the papers to file before the first day, the real cost of a failed posting illustrated by two Court of Cassation rulings from June and September 2026, and when hiring locally becomes the safer option. It complements our founder guide to setting up, banking, VAT and first hires in France and our walkthrough of surviving a URSSAF audit from abroad.
The stakes are higher than a paperwork fine. A posting built on fake or fraudulently obtained A1 social-security certificates can end in criminal court for concealed work and labour trafficking in an organised gang, as the Criminal Chamber of the Court of Cassation recalled on 9 June 2026 when it reviewed convictions against a labour-supply company operating between Spain and French farms. And the French customer who uses your posted workers is not a bystander: if it skips its monitoring duties, it pays your social-security debts alongside you, a rule the Second Civil Chamber applied again on 24 September 2026. Read both halves of the risk before your employee boards the plane.
I. Can you post your own staff to France, and which papers must be ready before day one?
A. Is your assignment really a secondment, and where does social security stay?
French law starts with a permission framed as a definition. Article L1262-1 of the Labour Code provides that “Un employeur établi hors de France peut détacher temporairement des salariés sur le territoire national, à condition qu’il existe un contrat de travail entre cet employeur et le salarié et que leur relation de travail subsiste pendant la période de détachement.” Three configurations qualify: posting staff to perform a service contract you signed with a French customer, moving staff between establishments of the same company or group, or posting staff to work for your own account in France without any French customer at all. The common thread is temporariness and a surviving employment link: the worker remains your employee, paid by you, returnable to your organisation. If the person is recruited to work permanently in France under the orders of the French operation, that is not a posting but a local hire, and the full French hiring regime applies instead, starting with the prior hiring declaration: Article L1221-10 states that “L’embauche d’un salarié ne peut intervenir qu’après déclaration nominative accomplie par l’employeur auprès des organismes de protection sociale désignés à cet effet.” Misclassifying a permanent local job as a posting is one of the fastest routes to a concealed-work prosecution.
Social security follows European coordination rules, not the employment contract. Inside the European Union, the European Economic Area and Switzerland, a posted worker can stay affiliated to the home-state scheme for up to 24 months provided the home institution issues an A1 certificate before or at the start of the posting, under Regulation (EC) No. 883/2004. The A1 is the document French inspectors ask for first: with a valid A1, no French social contributions are due on the posted salary; without one, URSSAF (the Unions de recouvrement des cotisations de sécurité sociale et d’allocations familiales, the French social-security collection agencies) can treat the worker as subject to the French scheme and bill contributions retroactively, plus surcharges. Outside Europe, affiliation depends on the bilateral social-security treaty signed with the worker’s home country, and where no treaty exists the worker generally falls into the French scheme from the first day, which changes the cost of the assignment completely. Apply for the A1 early in the home country, because posting staff while the certificate is still pending leaves the assignment exposed for every week of delay.
An A1 certificate protects only as long as it is genuine. The Court of Cassation recalled the European rulebook on 9 June 2026 in a case about Spanish A1 certificates used to supply labour to French farms: “les certificats A1 délivrés par l’institution compétente d’un Etat membre créent une présomption de régularité de l’affiliation du travailleur concerné au régime de sécurité sociale de cet État et s’imposent à l’institution compétente et aux juridictions de l’État membre dans lequel ce travailleur effectue sa prestation”, and this holds “aussi longtemps que ce certificat n’a été ni retiré ni déclaré invalide par l’Etat membre dans lequel il a été établi” (Cass. crim., 9 June 2026, No. 24-85.090). But the same ruling recalls the fraud exception built by the Court of Justice of the European Union: where the host-state institution has asked the issuing institution to re-examine fraudulently obtained certificates and the issuer ignores the evidence, the trial judge may set the certificates aside upon finding fraud, following the Altun case law. In the 2026 case, URSSAF investigators had gathered concrete evidence of fraud, asked Spain to re-examine, and the defendants stood convicted of concealed work and labour trafficking in an organised gang. An A1 obtained for workers who never worked in the issuing state, or kept after the 24-month limit, is not a shield but an exhibit.
B. Which declarations must reach France before your worker starts?
Every posting in the two main configurations, service contracts and intra-group moves, starts on a screen, not at the border. Article L1262-2-1 of the Labour Code requires that the employer “adresse une déclaration, préalablement au détachement, à l’inspection du travail du lieu où débute la prestation.” The declaration is filed on SIPSI, the Interior and Labour ministries’ online portal (sipsi.travail.gouv.fr), before the assignment begins, and it must be cancelled or corrected on the same portal if dates change or the posting is abandoned. The same article adds a second duty that foreign employers constantly overlook: the employer “désigne un représentant de l’entreprise sur le territoire national”, tasked with liaising with the control authorities for the duration of the assignment. The SIPSI declaration itself serves as the designation, with the representative’s identity, contact details and acceptance translated into French. Without a reachable representative, inspectors treat the posting as unsupervised, and the fine follows.
Posted workers are covered by a hard core of French employment law from the first hour: the statutory minimum wage (SMIC) and any higher sector minimum, maximum daily and weekly working hours, minimum daily and weekly rest, paid leave rules, health and safety, and equal treatment. Beyond twelve months on the same post, counting cumulative successive postings, almost the entire French employment regime applies except hiring and termination rules and supplementary pensions, unless the employer files a reasoned six-month extension on SIPSI before the twelve-month mark. The employer must keep time records showing each worker’s daily start, end and duration, produce payslips or equivalent proof of minimum pay for postings of one month or more, and hold all documents translated into French ready for inspection; in construction, each posted worker also needs a BTP identification card requested after the SIPSI declaration. These are not back-office niceties: inspectors can demand the papers on site, and failure to present French translations can suspend the service for up to one month by order of the regional authority (DREETS).
Short and one-off assignments have lighter but not empty formalities. Activities listed by the order of 4 June 2019, such as certain artistic, sporting, trade-fair or training missions, can be exempted from the prior SIPSI declaration and the representative requirement within strict duration caps per reference period, but the employer still has up to fifteen days to produce the control documents in French when inspectors ask. Check the list before assuming the exemption: most commercial, technical and care assignments do not qualify. And whatever the duration, the posted worker needs the right to be in France. EU citizens circulate freely, but a non-EU employee posted to France needs a work authorisation and, depending on length and nationality, the appropriate visa or residence permit. Posting a third-country national who already works for you at home does not waive French immigration law.
Keep the evidence for the whole assignment and beyond. Inspectors expect, for the entire posting, daily time records for each worker, and for postings of one month or more the payslips or equivalent documents proving minimum pay with all required mentions; for shorter postings any document proving minimum-pay compliance will do, but it must be translated into French. Payslips must show the French minimum rates actually applied, not the home-country salary converted at an optimistic rate, and overtime must be counted under French thresholds and premiums, a point our guide to overtime for a first French employee explains with the time-record rules labour courts enforce. Store the SIPSI receipt number, the A1 certificates, the representative’s acceptance letter, the customer contract and every payslip in one file your representative can open on a phone during an inspection. Controls often happen jointly, with labour inspectors checking papers on site while URSSAF auditors reconstruct contributions in the office months later; a file that answers the first inspection usually prevents the second procedure.
II. What does a failed posting cost, and when does the French customer pay with you?
A. How much does a failed posting cost the foreign employer?
Administrative fines are calibrated per worker and they add up fast. Article L1264-1 of the Labour Code provides that “La méconnaissance par l’employeur qui détache un ou plusieurs salariés d’une des obligations mentionnées à l’article L. 1262-2-1” is “passible d’une amende administrative”, under the conditions set by Article L1264-3. And Article L1264-3 sets the scale: “Le montant de l’amende est d’au plus 4 000 € par salarié détaché et d’au plus 8 000 € en cas de réitération dans un délai de deux ans à compter du jour de la notification de la première amende. Le montant total de l’amende ne peut être supérieur à 500 000 €.” Each missing SIPSI declaration, each missing representative, each set of untranslated documents is a separate count, multiplied by the number of workers. A ten-person team posted for a season without declarations can therefore face up to 40,000 euros per breach category, before any tax or social-security reassessment. The labour inspector records the breach, the regional director imposes the fine after adversarial proceedings, and the amount reflects the gravity, the employer’s behaviour and its resources.
Beyond fines, the administration can stop the work. When translated documents proving minimum pay, rest periods and maximum hours are missing or deliberately wrong, the DREETS can suspend the service for up to one month, lifted only once the breach ends. For a construction schedule, a harvest window or an installation deadline, a suspension costs far more than the fine. And behind the administrative layer sits the criminal one. Running people in France without registration, without declarations and without A1 cover is prosecuted as concealed work by concealment of activity: Article L8221-3 of the Labour Code treats as concealed work any profit-making activity carried on by a person who deliberately evades registration or social and tax declarations. The June 2026 case shows the ceiling: convictions for concealed work and trafficking in labour (marchandage) in an organised gang, prison sentences, and the managers held jointly liable for the collection agencies’ losses. No founder should read that ruling as distant case law: the fact pattern, foreign labour supplier, French farms as customers, A1 certificates as cover, is exactly what routine URSSAF and labour-inspectorate joint controls are designed to catch.
Social-security reassessment is the third bill. Where the A1 is missing, expired or set aside for fraud, URSSAF affiliates the workers to the French scheme and claims employer and employee contributions retroactively for the whole posting period, with late-payment surcharges and, in fraud cases, the specific anti-fraud surcharges. Posted workers without genuine home coverage can also claim the benefit of French minimum standards in court, including back pay to the French minimum and overtime. Add the project suspension, the customer’s lost schedule, and the reputational stain of a criminal conviction that follows the managers personally, and the economics of a cheap non-compliant posting collapse. Compliant posting costs a SIPSI filing, translations, a representative and proper pay; non-compliant posting risks fines, back contributions, suspension and prosecution.
Every sanction follows a procedure you can use. The labour inspector records findings in a report, proposes the administrative fine to the regional director, and the employer must be told which facts are alleged and which penalties apply before the fine is imposed; the decision can then be challenged before the administrative court within two months. URSSAF reassessments follow their own adversarial path, observation letter, contradictory phase, formal notice, then appeal to the amicable appeals committee and the judicial social-security court, the route our URSSAF audit guide maps step by step. Deadlines are short and strictly enforced from abroad, so appoint a French correspondent for service of documents on day one and diary every appeal date twice. Silence or late replies turn contestable fines into final debts.
B. When does your French customer pay for your breach, and how can it escape?
French law refuses to let the customer look away. Any client signing a service contract above the regulatory threshold must verify, when signing and periodically until the work ends, that its contractor complies with registration and declaration duties: Article L8222-1 of the Labour Code requires that “Toute personne vérifie lors de la conclusion d’un contrat dont l’objet porte sur une obligation d’un montant minimum en vue de l’exécution d’un travail, de la fourniture d’une prestation de services ou de l’accomplissement d’un acte de commerce, et périodiquement jusqu’à la fin de l’exécution du contrat, que son cocontractant s’acquitte : 1° des formalités mentionnées aux articles L. 8221-3 et L. 8221-5”. In practice the customer must collect the contractor’s vigilance documents, the foreign equivalent of registration proof, the SIPSI declaration details, the A1 certificates and the sworn statements, and renew the check every six months until the final invoice. A customer that files these papers without reading them is barely better protected than one that never asks.
A customer that skips vigilance pays the contractor’s debts. Under the rule applied in the September 2026 ruling, the client that breaches its monitoring duties is jointly liable for the mandatory contributions, penalties and surcharges owed by a subcontractor caught for concealed work. The Second Civil Chamber restated it on 24 September 2026: “Selon l’article L. 8222-2, alinéa 2, du code du travail, le donneur d’ordre qui méconnaît les obligations de vigilance énoncées à l’article L. 8222-1 du même code, est tenu solidairement au paiement des cotisations obligatoires, pénalités et majorations dues par son sous-traitant qui a fait l’objet d’un procès-verbal pour délit de travail dissimulé.” (Cass. civ. 2, 24 September 2026, No. 24-13.124). The verified text of Article L8222-2 confirms the mechanism: anyone who breaches the vigilance duties is held jointly liable with the reported offender for taxes, contributions, penalties, recovered public aid and unpaid wages. For a foreign supplier, this means the French customer has a direct financial incentive to audit your posting file before signing, and sophisticated customers now demand the SIPSI number and A1 copies in the tender.
The same ruling hands the customer, and indirectly the supplier, the defence playbook. The Court confirmed that the client may attack the regularity of the reassessment issued against the contractor: “le donneur d’ordre peut invoquer, à l’appui de sa contestation de la solidarité financière, les irrégularités entachant le redressement opéré à l’encontre de son cocontractant du chef de travail dissimulé.” In that case the appeal court had annulled the URSSAF letters because the control aimed at detecting illegal work had not been notified to the contractor in a document signed by the collection agency’s director, as the applicable social-security procedure required, and the Court of Cassation rejected URSSAF’s appeal. The practical message for foreign employers is twofold: keep your own file clean enough that no reassessment can stand, and know that your customer’s lawyers will scrutinise URSSAF’s procedure as closely as the facts. Joint liability is joint: a procedural flaw in the contractor’s reassessment can defeat the claim against the customer too. Conversely, a customer facing a joint-liability notice will immediately turn against the supplier for breach of the contract’s compliance warranties, so draft those clauses, and the indemnity behind them, before the posting starts rather than after the control.
Conclusion
Secondment is lawful, flexible and closely watched. It works when the employment link stays genuine, the A1 certificate is real and current, the SIPSI declaration precedes the assignment, a representative answers inspectors in French, pay meets French minimums from the first hour, and documents are translated before anyone asks. It fails expensively when any link breaks: up to 4,000 euros per worker per breach within a 500,000-euro ceiling, suspension of the work for a month, retroactive French social contributions, and criminal prosecution for concealed work and labour trafficking where A1 certificates cover a fraud, the exact scenario the Criminal Chamber dissected on 9 June 2026. The French customer shares the exposure through joint liability for contributions and penalties whenever it neglects vigilance, tempered by a real right to challenge URSSAF’s procedure that the Second Civil Chamber confirmed on 24 September 2026. Foreign founders choosing between posting their own people and hiring locally should compare honestly: short, skilled, supervised assignments with clean papers favour secondment; permanent, customer-facing or large-scale staffing in France favours a local contract under a French entity. Whichever route you take, file first, translate everything, and keep the A1 certificates where an inspector can see them.