Can I be forced to work while on medical leave?

The FMLA generally prohibits an employer from interfering with or retaliating against your medical leave.  Assuming that you were approved for FMLA leave and assuming further that you submitted proper notice, you should consult with a FMLA lawyer.  As in all cases, the facts, details, and circumstances will dictate the viability of a successful lawsuit or other remedial option.  For instance, when you ask if you can "be forced to work on mecial leave," what do you mean by "forced?"  If you were granted FMLA time, and the employer threatened to fire you for exercising such time, then you might have an FMLA claim.