You mentioned that your baby was premature...did you have to take leave under medical emergency circumstances and under doctor's orders? If so, under CA law, you "may" have a case against your employer.
The following info is from: http://www.sahra.org/asklegalarch.htm
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Question:
Is it legal to terminate someone who is on pregnancy disability?
Answer:
It is difficult to answer this question based on the limited amount of information provided. Pregnancy Disability Leave implicates other leaves requirements such as Family Medical Leave and California Family Rights Act as well as various federal and state laws regarding disability discrimination.
In the broad sense, California is an at-will state and unless the employee is contractual or must otherwise be terminated only for cause, she may be terminated at any time. That said, there are many exceptions to that rule. First, you may not terminate an employee on any type of disability because of their disability. Additionally, an employee who takes Pregnancy Disability Leave must be reinstated to the same or similar position when she returns to work unless one of the two following exceptions applies:
(A) That the employee would not otherwise have been employed in her same position at the time reinstatement is requested for legitimate business reasons unrelated to the employee taking a pregnancy disability leave or transfer (such as a layoff pursuant to a plant closure).
(B) That each means of preserving the job or duties for the employee (such as leaving it unfilled or filling it with a temporary employee) would substantially undermine the employer's ability to operate the business safely and efficiently.
Note that it is very difficult to prove that preserving the employee’s position would substantially undermine the employer’s ability to operate the business safely and efficiently. As a result, unless the employee would be terminated due to lay offs or other clearly legitimate reasons, it is best to error on the side of caution.
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For another site with an actual synopsis of the California Maternity Leave laws see:
http://www.ehow.com/list_###-###-####_california-maternit...
I strongly recommend that you contact an employment attorney in your area for further consultation.
I also recommend you contact your local La Leche League for interpretation of your state's breastfeeding statutes/laws. Many states have breastfeeding protection laws as well, including California. From the information I found online, your employer must/is required to make arrangements and allowances so you can breastfeed and/or pump for your child. A representative from LLI will know in more detail what that would mean for you specifically. To find a coordinator go to www.llli.org .