In November 2025, Slovenia made a winter bonus mandatory for all employees and required employers to pay it for the whole of 2025, even though the law only came into force seven weeks before the end of the year. In September 2026, the Constitutional Court ruled that the bonus itself is constitutional, but that charging employers for the months before the law existed was not.

The ruling leaves employers in an unusual position. The money has been paid and cannot be reclaimed from employees. The open question is whether employers can now turn to the state for compensation.

What happened

The Act on the Right to a Winter Bonus (the “ZPZR”) entered into force on 20 November 2025. It requires employers to pay every employee a winter bonus of half the Slovenian minimum wage each year, EUR 638.86 for 2025, by 18 December. Employees who work part of the year or part-time receive a pro rata amount.

Because the law contained no special rule for 2025, entitlement and amount depended on employment throughout the calendar year. The obligation therefore also covered 1 January to 19 November 2025, when the law did not yet exist, as well as employees who had already left before it came into force. The Ministry of Labour confirmed this reading in guidance published on 24 November 2025, and the Constitutional Court later adopted it.

The sums are significant. For an employee who worked the whole year, almost 90% of the bonus relates to the period before the law took effect. Media estimates put that share for the private sector at around EUR 428 million, and the government did not dispute the claim before the court that the total cost was “almost half a billion euros”.

The Constitutional Court’s decision

In decision U-I-189/25 of 24 September 2026, the Court held that a mandatory winter bonus does not disproportionately restrict employers’ freedom of enterprise. The bonus therefore stays in place for 2026 and future years.

However, the Court found the relevant provisions unconstitutional to the extent that the 2025 bonus takes into account employment before 20 November 2025. This breaches Article 155 of the Slovenian Constitution, which prohibits laws from having retroactive effect.

The Court did not annul the provisions. It issued a declaratory ruling only, because annulment would have undermined employees’ legitimate expectation of keeping money paid under a statutory entitlement. As a result, employers have no basis to ask employees to return the payments.

Why retroactivity matters

Under the Slovenian Constitution, laws may not apply retroactively. By way of exception, a statute may give individual provisions retroactive effect, but only where the public interest requires it and acquired rights are not affected. The prohibition is at its strongest where a law attaches new obligations to facts that are already complete and which those affected can no longer change.

The 2025 winter bonus is a textbook example. An employer learned in November that it had to pay a former employee, who worked from January to July, a share of a benefit that did not exist at the time. Had the rule applied only going forward, the employer could have adjusted its budget, reward policy or prices.

The Court stressed that any public interest justifying retroactivity must be identified in the legislative process itself. Here, the legislator did not even recognise that the law operated retroactively. The Court also noted that the 2025 bonus “is not a negligible financial burden which businesses could be assumed to absorb easily without the opportunity to prepare in advance and adjust their business plans” (our translation). The duty to justify retroactivity was therefore particularly strict.

Legal certainty and predictability are core elements of the rule of law. Businesses plan budgets, headcount and pricing on the basis of the rules in force. If the state can change the cost of work already performed at the end of the year, every business plan becomes provisional.

Can employers claim damages from the state?

Article 26 of the Slovenian Constitution gives everyone the right to compensation for damage caused by the unlawful conduct of a state body. In principle, this covers both the legislature and the executive. However, a finding that a law is unconstitutional is not enough on its own: the courts require a qualified, serious breach. These are complex legal questions without clear-cut answers, and several issues will be decisive.

First, the seriousness of the breach. The Constitutional Court’s case law on retroactivity is long-established and clear. It may also matter whether the legislator was warned about the retroactive effect during the legislative process and ignored the warning.

Second, the role of the executive. The ministry’s guidance reinforced the retroactive reading, compliance was checked by labour inspectors, and non-payment was subject to fines, even while the constitutional challenge was pending. Employers had little choice but to pay.

Third, the right to property. The European Court of Human Rights interprets the European Convention on Human Rights in light of the rule of law and legal certainty, and protects legitimate expectations regarding the peaceful enjoyment of possessions under Article 1 of Protocol No. 1. The Slovenian Constitutional Court did not examine the retroactive part of the law from this angle, nor under the constitutional right to private property. Whether forcing employers to fund a retroactive entitlement from their own assets also interfered with their property rights remains an open question.

Finally, damage and time limits. Loss would have to be proven employer by employer and would cover the part of the bonus attributable to the period before 20 November 2025, plus payments to employees who left before that date. Claims are subject to a three-year limitation period from when the claimant became aware of the damage. It is uncertain whether time runs from payment in December 2025 or from publication of the Court’s decision, so the earlier date should be assumed.

What this means for employers

• The winter bonus is here to stay: budget for it every year, payable by 18 December.
• Payments made for 2025 cannot be recovered from employees.
• Collect payroll records for the 2025 bonus now and calculate the portion attributable to the period before 20 November 2025.
• Take advice early, as the limitation period may already be running from December 2025.

Conclusion

The decision confirms that the prohibition of retroactivity binds the legislator even when it acts to benefit employees. For employers that paid the 2025 winter bonus, it opens the door to a possible compensation claim against the state, but the path is legally demanding and time-sensitive. Any decision to pursue a claim should rest on a careful, case-by-case assessment.