As a union member going in you know you have to pay dues so nothing was forced on you. Almost always the union will spend those dues to your unions benefit whether that be bribing pro union candidates or whatever. Consider it part of your benefits package whether you think of it positively or negatively. Don't take the job if you don't agree with it.

Shareholders own the Corp. ANY money paid out politically is done so without the approval of minority shareholders. Even if given a vote show me where minority shareholders have ever won a vote against the majority shareholders in a large corp.

As for non-union employees...if there are cuts to pay, cuts to benefits, layoffs, etc and the amount of political donations does not decrease then you paid for it against your will. That was not negotiated going in. You got F'd and there's nothing you can do about it.