As a strong supporter of unions, that's the end of my donations. I've probably donated fewer than a dozen times, but definitely more than five or six. I felt reasonably good about it and went on with my day, no hesitation about supporting them. That's done.
Fwiw, unions often have support pages where you can donate or buy merch to support. One of my favorite tshirts advocates for a union that was trying to form at a huge retail chain (looking at you Starbucks Workers United). I did a quick search and this[0] appears to be them.