I know a local teacher who had union thugs remove candidate signs from her front yard. When she objected, they told her that as a union member (forced) she could not support that candidate.
Know the scenario well. Also know how to sign the form to keep them from donating your money to a candidate you oppose. And what legal actions to take when the above scenario happens. There are actions to take but its tiring and time consuming at the expense of classroom prep etc. it also creates a very hostile work environment