For all that the US Constitution mandates the separation of church and state, the two do overlap in quite a few areas. (Just look at your currency, with its slogan of “In God We Trust”.) One of those areas is taxation: the US government subsidizes churches to the tune of many billions of dollars per year by giving them tax-exempt status. One conservative estimate put the sum at $71 billion, but the fact is that no one really knows what the number is.
It’s important to note that the tax exemption for churches and other religious organizations is not embedded in the Constitution. The First Amendment guarantees freedom of religion, but that’s free as in love, not free as in beer. Taxation is a purely secular affair, and by default it applies to everybody equally, whether they’re a religious institution or not. It would be unconstitutional to single out religious institutions to make them paymore tax than anybody else, but the government has every right to stop giving them special tax-free privileges. (One example: the Mormon church owns a theme park in Oahu which pays no federal taxes. That’s even after a Hawaii court found it to be “not for charitable purposes”, and therefore subject to local property taxes.)