Under Federal laws, the employer is not required to grant FMLA to any employee for the first 12 mos. of their employment. I was once terminated from a job for taking a month off when my husband was on an ICU for 23days. FMLA laws are regulated by US Dept. of Labor.
I am a little fuzzy about our situation. I know that my employer is required to accommodate me under the Americans with Disabilities Act (ADA), because Crohn's is covered under ADA.That was reaffirmed under 2008 amendments. You can contact the Equal Employment Opportunity Commission for more specifics regarding the ADA. EEOC regulates discrimanation related to ADA. You can find info about when to tell your employer about your disability on the page link below. Other pages on this site define the term disability.
I hopes this helps. If I hadn't told my employer during my interview for the job, I would probably wait until after the my 1 year anniversary if I was working in a right to work state in a non-union job. I would refer to local laws to see if they had any employment at will laws, under those laws they can terminate you without explaination, or use another excuse. If you are union you may have a right to an explaination regardless.