So priests are paid by the state then?
As nobody's bothered to answer the simple question so far, I'll try to. The priests who teach religion at schools and those who work as chaplains with the army, at hospitals etc. get regular salaries from the state. Those who stay at parishes, are supported by the faithful - they collect money during mass, for funerals, weddings etc. and get a salary out of this money, it's controlled by the curia.
Tusk's announcement was not about taxing the salaries but about pension and health service contributions (ZUS), which to date have been covered by the Church Fund (Fundacja Kościelna), established in 1950 as compensation for the lands and property taken from the Church by the state. Since 1990, the Church has been recovering the lost property or its equivalents and the Fund during this time has been financed solely by the state budget. So Tusk now aims to liquidate the Fund, and the priests would have to pay the ZUS contributions by themselves, or the curias would have to cover it.
The CC is not opposing the idea. They say they're ready to work out new solutions.