Employers don't have to, at least in the U.S. Lots of people I know have used up their PTO and sick days for maternity leave. There is also FMLA, which is unpaid but guarantees you'll still have a job after 12 weeks. In some cases, like in the parent comment, they'll figure out a way to cut you loose.
My wife took FMLA for six weeks. Law or no law, HCA happily told her she had the right to apply for another job at another center when she got back. With no guarantee of the same pay. Of course, she ignored them and didn't go back, but we didn't sue either, as that wasn't feasible. Big companies can get away with a lot that isn't legal or ethical.
Oh, for some reason I was under the impression they were. Thanks for clarifying. A quick Google search seems to show that a few states require paid leave for a short period at a discounted wage.
