Woke up sick so I called into work. Boss told me I’m getting written up because “this calling in thing is getting out of hand.” I haven’t missed work for over two months and that was because of a COVID scare/test.

He claimed that I call in every 2 weeks, and then said he hasn’t called in for 18 years. He is already on a “last strike” from the union heads, and I’m definitely going to be reporting him for this. My question is, do I call the union immediately? Or do I wait until I actually get written up to use as physical evidence?