https://en.wikipedia.org/wiki/Church_tax

> The church tax is only paid by members of the respective church, although the concept of "membership" is far from clear, and it may be asked what right the secular state has to tell the faithful what contribution they should make to their own denomination. People who are not members of a church tax-collecting denomination do not have to pay it. Members of a religious community may formally cease to be considered members by making a declaration to state (not religious) authorities, ending liability to pay church taxes. Some religious communities refuse religious marriages and funerals to members who leave.

Is it harder than implied to make that declaration?