The Union (and all its members) are barred from attempting to organize a work slow down. You are in STATUS QUO! The amounts of OT being picked up system wide should not change. The fact that it changes coupled with pilot's telling other pilot's NOT to take any OT is a violation of STATUS QUO!
Doesn't matter who's telling pilot's to do that!
Unions are OBLIGATED to tell their pilots to continue on as normal (ie, Statue Quo) during negotiations, which began the moment union sent their Section 6 notice. Otherwise, it would be OK for someone to tell the company to ignore other norms they have been doing! They can play your silly game too if they wanted to stoop down to your level!