If international travel is required for your work, I imagine not being vaccinated would preclude you from performing your duties so firing you is probably defensible. Especially if you work in an at-will state, where you can be fired for any and no reason at all. You might have a case but I think they would likely win.
Let them fire you, or get the shot, but definitely don't quit unless you can afford it. If you can afford it, piss on their rug before you walk out
(post is archived)