Punish them with fines (and jail time if suitable) and take away their 501(c)3 status. Remove their government contribution as well.
Should be far more so--the justification for the government sitting in judgement on what is said in church about government rests solely on the tax deduction argument. Enact a flat tax or a sales tax--either of which eliminates that deduction--and the rationale for outlawing chuch discussion of politics vanishes.