Federal law prohibits experimental treatments/shots being mandatory. But that won't stop them from trying really hard, or trying to convince you otherwise. Perhaps they'll be 'creative' and find another way to discharge the non-compliant employee......lots of 'reasons' can start to emerge.

Here's a link re: cannot mandate emergency use therapy: https://childrenshealthdefense.org/defender/under-federal-law-can-your-employer-make-you-get-covid-vaccine/