Can my employer contact me to lay me off while I'm on a leave of absence(had a baby)?

Technically “yes” – the employer in an “at will” State, like California, can fire you for any reason at any time.  However, I am always suspicious when an Employer decides to “randomly” fire a woman who is taking time off for maternity leave.  It would be a good idea to speak with an attorney about the other facts surrounding your employment because you may have a good employment claim (for example under FEHA).