S.W.
FMLA does not apply to companies with fewer than 50 employees. http://www.dol.gov/dol/topic/benefits-leave/fmla.htm
I would suggest getting a letter from your doctor describing your need for surgery and needed recovery time. I would bring the letter and have a private talk with your plant manager about what the best timing would be, what you can do to make this easiest for them, etc. Remind your manager of your 12 years of service and your commitment to staying more years after you get this medical issue resolved.
In the end, though. They can legally terminate you for any, or no, reason. Sorry.