Legal Question in Medical Leave in Massachusetts

Re: Possible Termination

If the written warning pertains to conduct covered under the company policy, yes. Pregnancy is not a shield for things they could write you up for anyway.

The problem is that they might have a mixed-motive, something that can be notoriously difficult to prove. A local lawyer could give you a better idea of what the courts do in your state, but at the very least, you need to start documenting everything and keeping copies of documents that prove what you're saying and lists of people who have direct knowledge of what is going on.