Confiscations of Mendizabal is a 
Spainish decision.
It gives 25.000 ducats to Spain as well as 10.5 prestige. In exchange Spain's relation with 
Papal States decreases by -50. All pops in Spain that support conservatism will gain 4 militancy and the entire population will become 15% more in favor of Atheism.
The only requirement is to have invented Ideological Thought, which can be researched from day 1. One have to weight the risk of revolt against the extra money input and prestige.