” . . . Perhaps the mask has taken on a totemic significance for them.”
As I see it, this is an issue of power and control. Many union members and officers are dyed in the wool Democrats, Progressives and Leftists. But, they also are significant contributors to political candidates. By demanding the mask edicts be enforced, the unions are sending a message that continued political support comes with a cost - and the cost here is bowing to the unions exercise of power over helpless children. It seems to be the way in which the unions can demonstrate to their members that they have power to influence events in real time.