Kirchensteuer, literally "church
tax", was introduced in
Germany in 1933 by
Hitler through an agreement with the
Vatican. The agreement also made a place for religion at universities and schools.
The Federal Republic of Germany did not discontinue the agreement, which means that everyone belonging to the big two churches has to pay up to nine percent of his income in taxes which are collected by the state. The Kirchensteuer is tax-deductible, so you actually don't pay the full amount, only most of it.
The tax may explain why the number of members in the two big christian churches in Germany is decreasing, since the tax is not applicable towards people with no or rare religions. It is applicable towards unemployment compensation though, so a church member gets higher relative compensation, although more than 43% of the employed population doesn't pay the tax anymore.