Church tax was quite normal in earlier times.
One part of your taxes went to the Church and the other to the King.
In modern times, many Western European countries have governments which continue to fund churches, but through the general taxes and not through a special church tax which the governement collected on behalf of the church. In Germany, the church tax has not been abolished yet and is collected by the state on behalf of the church. In other countries, the church tax was abolished and included in the general tax. (Another way for the governments to seize power over the churches, probably.) As Gorazd says, it is the same system for every recognised religious entity.
For a doctrinally immensely corrupt (from a trad Catholic perspective) hierarchy like the German Catholic hierarchy, it is a blessing to receive that tax since they continuously get funding for their Modernist activities. The church there is rich and that allows it to pose as a body full of life, which is contrary to reality. The RCC in Germany is as dead as the RCC in Holland and is a rotten corpse beneath the golden cover.
However, they fear that many Catholics will opt out and then they resort to intimidation and force to keep the donors and their wealth. The soul has been out of the equation for years.
Probably the best example there is of "pay, pray and obey", except for the prayer part of it. It should be "pay, modernize, destroy, ecumenize and obey" in stead.