Temp work and medical leave?

Because labor laws differ depending on what country/province/state you are working in it is hard to give you a definitive answer. That said, if you are in the US, and working in a "work at will" job, which most are, then you can quit/leave, or be fired for any reason or no reason at all, with or without notice. Exceptions to this may be FMLA related issues. The link below is to the government FMLA website. If you feel your situation is covered by it, then you may have some recourse. It is best to try and speak with the government agency that oversees employment law in the location where you work for a good answer.