ADA is only helpful if the employer abides by it. I checked into it and the only remedy they do is to sue for money to replace what you would have earned if you are fired. They don't get your job back for you. They have to go through negotiations before they can sue. Also there is a very limited time span from when you lose your job to when you can no longer sue.

In my case, I would have had to refuse to sign the letter and not be allowed to work for me to have ADA support.