You should definitely report this to the union, and review your local labour protections (with union help or otherwise). Chances are this isn’t legal.
Beyond that, you should also consider finding alternative employment - a response this unabashedly heavy-handed should tell you that if this prick hasn’t already marked you for mentioning a union, he’ll find a reason to make your life hell soon enough.
You should definitely report this to the union, and review your local labour protections (with union help or otherwise). Chances are this isn’t legal.
Beyond that, you should also consider finding alternative employment - a response this unabashedly heavy-handed should tell you that if this prick hasn’t already marked you for mentioning a union, he’ll find a reason to make your life hell soon enough.