Start with giving them this letter.
Once given to them, if you are fired, smile at the money they are going to lose in a civil lawsuit to you.
Smart employers will pass this letter to their legal council, and when their council informs them of the multitude of laws they will be violating by forcing the "vaccine", they should quickly back down.
Also, you can get religious exemption and if they require a "clergy" letter, you can have an ordained minister write it. Getting ordained can be as easy as getting your pet certified to be a service animal 😉