Short answer
There is no single “country of employment” test. A cross-border assignment requires three decisions.
First, identifies the law governing the employment contract. A temporary assignment does not itself change the habitual workplace, and a choice-of-law clause cannot remove otherwise applicable mandatory protection.
Second, for a genuine posting under , the host Member State's mandatory package applies alongside the contract law. It covers working time, leave, remuneration, safety, equality, specified accommodation and expense rules, and temporary-agency conditions. After 12 months—18 following a motivated notification—most additional host employment terms apply.
Third, independently chooses one social-security system. Home-state affiliation may continue for a qualifying posting lasting no more than 24 months. An A1 certificate addresses that social-security question; it does not prove that host-state wage or working-condition rules are inapplicable.
Start with the employment contract, not the travel itinerary
For contracts within Rome I's scope, Article 8 protects an employee from losing mandatory rights through a choice-of-law clause. Without an effective choice, the starting point is the country where, or from which, the employee habitually performs the contract. A temporary move is deliberately treated differently from a permanent change.
“The country where the work is habitually carried out shall not be deemed to have changed if he is temporarily employed in another country.”
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The sending State's law may therefore continue to govern the contract. Article 8 also preserves non-derogable employee protection under the objectively applicable law, while the Posted Workers Directive creates a specific host-state floor. Denmark is not bound by Rome I, so its private-international-law route must be assessed separately.
Is the worker genuinely posted to the host State?
Directive 96/71 covers three basic structures: an employer providing services under its direction to a host client; an intra-group posting; and a temporary-work agency supplying a worker to a host user undertaking. The employment relationship with the posting employer must continue. A posted worker must also work for a limited period in a Member State other than the State in which that person normally works.
Labels are not conclusive. Article 4 of requires an overall assessment, including genuine sending-state activity, the normal workplace, duration, expected return, and responsibility for travel and lodging.
The Grand Chamber illustrated the territorial limit in Dobersberger, Case C-16/18. Workers on international trains performed significant work and began or ended shifts in the sending State. Their work lacked a sufficient connection with the transit State for the old Directive's posting rules to apply (paragraphs 31–35). Crossing a border is not enough. Sector-specific legislation, especially for road transport, must also be checked.
Which host-state protections apply from day one?
For a genuine posting, national legislation implementing Article 3 must guarantee the host State's applicable terms on an equality basis, regardless of the contract's governing law.
“Member States shall ensure, irrespective of which law applies to the employment relationship, that undertakings as referred to in Article 1(1) guarantee, on the basis of equality of treatment, workers who are posted to their territory the terms and conditions of employment” laid down in the Member State where the work is carried out.
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The listed matters are maximum work and minimum rest periods; minimum paid annual leave; remuneration including overtime; hiring-out conditions; health and safety; protections for pregnancy, recent childbirth, children and young people; equality and non-discrimination; employer-provided accommodation; and specified travel, board and lodging allowances or reimbursements. National law and universally applicable—or otherwise qualifying—collective agreements determine the concrete amounts and conditions. More favourable contractual or sending-state terms remain possible.
“Remuneration” is not the same as refunding assignment costs. Posting allowances count as remuneration unless they reimburse expenditure actually incurred. If employment terms do not identify the reimbursed part, the current Directive treats the whole allowance as reimbursement.
In Sähköalojen ammattiliitto, Case C-396/13, the Court examined the earlier “minimum rates of pay” wording. It accepted transparent, binding host collective-agreement classifications and certain allowances, while excluding accommodation costs and meal vouchers (operative point 2). Directive (EU) 2018/957 later broadened the term to “remuneration”, but each payment's legal character still matters.
Narrow qualifications for initial installation and some very short or non-significant work must be verified in the host State's transposition, not assumed.
What changes after 12 or 18 months?
Long-term posting does not simply convert the contract to host law. Article 3(1a) instead expands the mandatory host package.
“Where the effective duration of a posting exceeds 12 months, Member States shall ensure, irrespective of which law applies to the employment relationship,” that posted workers receive, in addition to Article 3(1), all applicable host-state terms and conditions of employment.
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A motivated notification extends the threshold to 18 months. The expanded package excludes procedures and conditions for concluding and terminating the employment contract, non-compete clauses, and supplementary occupational pensions. Replacing one posted worker with another on the same task at the same place does not restart the clock; their periods are cumulated for this rule.
Social-security affiliation is a separate 24-month test
Regulation 883/2004 normally applies the legislation of the Member State where employed activity is pursued. Article 12(1) creates a specific exception:
“A person who pursues an activity as an employed person in a Member State on behalf of an employer which normally carries out its activities there and who is posted by that employer to another Member State to perform work on that employer's behalf shall continue to be subject to the legislation of the first Member State, provided that the anticipated duration of such work does not exceed 24 months and that he/she is not sent to replace another posted person.”
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, Article 14, adds that the employer must ordinarily perform substantial activity in the sending State, beyond internal management. The direct employment relationship and work on that employer's behalf must continue.
In Team Power Europe, Case C-784/19, the Grand Chamber held that recruiting temporary workers in the sending State was insufficient. A temporary-work agency also had to carry out a significant part of its worker-assignment activity for user undertakings established and operating there (operative part). The judgment is specific to agency work, but it underscores that a registered office or payroll operation alone cannot manufacture home-state coverage.
The 12/18-month employment threshold and 24-month social-security threshold answer different questions. A worker may remain insured in the sending State while already benefiting from the expanded host employment package.
What does the A1 certificate decide?
The competent institution can issue an A1 certificate showing which Member State's social-security legislation applies. In Alpenrind, Case C-527/16, the Grand Chamber confirmed its institutional effect:
An A1 certificate “binds not only the institutions of the Member State in which the activity is carried out, but also the courts of that Member State.”
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That rule presupposes a genuine certificate. In Case C-421/23, decided on 23 January 2025, the Court required dialogue and conciliation where purported A1 documents were suspected to be false. Once the alleged issuer confirmed non-issuance, the documents were not A1 certificates and had no binding effect. Dialogue still governed applicable legislation and any final fraud finding.
Crucially, the A1 certificate does not select the employment contract's governing law, determine whether Directive 96/71 applies, or displace host remuneration and working-condition rules. Treating it as a complete “permission to work under home law” confuses distinct legal regimes.
A practical assignment check
Before work begins, record:
- the employer, client or user undertaking, service structure, place of normal work, and expected return;
- why the work has a sufficient connection with the host State and qualifies under one of Article 1(3)'s posting models;
- the objectively applicable contract law under Rome I and any more favourable contractual rights;
- every host Article 3 term, relevant collective agreement, and the treatment of each wage, allowance, and reimbursement component;
- the 12-month date, any motivated extension to 18 months, and earlier workers doing the same task at the same place;
- the social-security basis, employer's substantial sending-state activity, 24-month limit, replacement history, and A1 status; and
- host declarations, document-retention duties, sector-specific rules, and available enforcement routes.
Conclusion
The protection is cumulative. Contract law supplies the framework; the Posted Workers Directive adds immediate and, for long postings, expanded host terms; social-security regulations select one contribution and benefit system. Territorial connection, wage components, employer substance, replacement, and A1 status can each change the result. A reliable assessment runs all three tests and keeps their clocks separate.
Sources
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This article provides general legal information, not advice for a specific matter. Laws, facts and procedural deadlines may change the result. Follow the linked primary sources and obtain local advice before acting.