Barry, I found this link if you want to check it out--
http://www.eeoc.gov/facts/fs-ada.htmlTo summarize it though, Christine is right on. I see people let go every so often when they are sick (with cancer, MS, even chronic laryngitis.) I work in a call center so speech issues will come up every so often.
Not sure if state law will cover you, so an attorney may be helpful.
What a big hassle it is when you've got cancer to deal with! Will your employer possibly grant you a temporary leave of absence to heal and improve your speech? My HR department will grant these and automatically submit information up for ss disability. It sounds like your employer is trying to work with you by giving you until January and allowing you to work in the meantime.
I sure hope you can find a easier resolution without having to spend the money and energy on an attorney. I really wish you the best of luck.
