Like MiniD said, that's legal.
When I was activated for the first Persian Gulf war, I was away from my job for 8 weeks. The only gurantee you have with your employer is getting your job back.
When I returned, they'd hired someone else and claimed too bad. The National Guard showed up, leaned on the manager real good and pointed out the law. Rumor has it, they were "magically" audited that tax year too
