First off, the First Amendment only applies to government and the Commons, not to the private sector. Congress can't abridge your right of free speech, but your employer damned well can.

Secondly, it's interesting that you say the offending action was taken by a member of management at the insistence of someone from your own union. Only goes to show why a lot of people, myself included, have little use for unions. Just amounts to working for two sets of bastards instead of only one.

Fuck 'em all. Be self-employed. Play music. Mow lawns. Paint houses. It doesn't matter. Just don't work for the sonsabitches.