There's more about it here on the BBC. The story has appeared all over the world, too; it's not just something Dawkins has cooked up.
In summary, it appears that there's a 200 year-old law in Germany whereby if you are a Roman Catholic, Anglican or Jew then you get taxed an extra amount. That extra amount then goes to your church and compensates the church for the nationalisation of church properties back in the 1800s. Some people are against this and so the RC church announced that if you don't pay the tax, you don't get to join in. Which sounds rather un-Christian but there you go.
I'm not surprised the churches are all in favour of this tax though. The German RC church made five BILLION Euros out of it last year, and the Anglicans slightly less at a mere four and a half BILLION. It doesn't say how much Judaism made.
Nice little earner, isn't it? If they had to go back to just relying on the take from collection plates and jumble sales I suspect they'd be looking at a significantly smaller take.