Doctrine and case law have already repeatedly defended that the special tax on secret commissions has the character of a (criminal) sanction. This means that a judge can marginally verify the proportionality within his unlimited control. This control is prescribed by the Constitution.
The judge is allowed to reduce or abolish the special tax on secret commissions to the extent that it constitutes a disproportionate penalty in comparison to the misconduct by the taxpayer. A judge has to be able to control everything that belongs to the appreciation of the tax administration.
To the extent that a special tax on secret commissions embodies a sanction, the requirements of the European Convention on Human Rights imply that the court must at least have the competence of appreciation that the tax administration also has.
Recent case law confirms this view.