There are multiple states in the United States that allow for “one-party consent” when it comes to recordings. To keep it simple (and keep in mind, I’m not exactly a lawyer), it means that if you want to record someone you’re in a conversation with, you can do so without informing them (assuming you’re part of the conversation, hence the “one-party”).
Now, I’m not here to debate the ethics involved here, but when you’re dealing with an asshole supervisor, it’s a handy law to have in your back pocket: