The Constitutional Court facing its limits: how far can the unconstitutional be maintained?

When the legislator crosses the red line

Despite repeated warnings, it is still the case that the legislator adopts tax laws that are contrary to the Constitution. Several years later, the Constitutional Court intervenes to correct the situation… by annulling the disputed provision.

The problem: to avoid budgetary and administrative chaos, the Constitutional Court increasingly chooses to maintain the effects of the annulled law, sometimes even for taxes that have already been established. This legal sleight of hand leaves the door open for tax adjustments based on provisions that have nevertheless been declared unconstitutional.

A striking example is the Fairness Tax – a tax which, despite its name, has distinguished itself neither by its legality nor by its fairness.

An annulment… with variable geometry

Introduced in 2013, the Fairness Tax targeted certain companies distributing dividends while significantly reducing their taxable base. 

On 1 March 2018, the Constitutional Court annulled it. However, it maintained its effects for assessment years 2014 to 2018, in the name of budgetary balance and to prevent widespread litigation. 

The tax authorities saw this as a green light to continue taxing, auditing and adjusting, even after the annulment, as long as the relevant assessment year fell within the covered period. 

However, the French-speaking Court of First Instance in Brussels recently put a stop to this interpretation: in a judgment of 28 April 2025, it recalled that only taxes already established at the date of the annulment can be maintained. Subsequent adjustments are illegal. 

There was no concrete legal basis for an adjustment relating to the Fairness Tax carried out after 1 March 2018 for the 2018 assessment year. 

Conversely, companies that were properly assessed before the judgment remain liable.  

Key takeaways 

Under the guise of avoiding litigation, the Constitutional Court has, in practice, fostered legal uncertainty. 

This recent judgment recalls a fundamental principle: once a law is annulled, no new taxation can be based on it. Only taxes already established may, exceptionally, be maintained. 

It is also important to keep in mind that the State may be held liable within a period of five years from the date the damage is known, either the date of the judgment or the date of the assessment. 

And the Fairness Tax is not an isolated case. The first version of the annual tax on securities accounts is another emblematic example. 

Golden rule: if a tax is annulled, the tax authorities cannot revive it, not even partially.

Have you been subject to an adjustment based on a provision that has now been annulled?

Do not hesitate to contact us: we will analyse your situation, explore possible legal options and assist you in contesting or appealing, if necessary.