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

The church tax is only paid by members of the respective church. People who are not member of a church tax-collecting denomination do not have to pay it. Members of a religious community under public law may formally declare their wish to leave the community to state (not religious) authorities. With such a declaration, the obligation to pay church taxes ends. Some communities refuse to administer marriages and burials of (former) members who had declared to leave it