I’d tell ‘em, “Let’s make a deal!” Unions can have collective bargaining rights but, in return, they give up their ability to contribute to the campaigns of those who will be in any way involved with the bargaining process.
It completely subverts the collective bargaining system when those on one side can give money to those on the other side of the negotiations. If it were a shipyard and not a school board, or county commission, etc. it would be bribery pure and simple.
Collective bargaining works because the two parties on different sides. It stops working when one side can give the other side money, gobs of money, to keep them in their bargaining position.