Boss Wants My Wife To Be Demoted Because Of Her Being Pregnant?

First time posting here, so I’ll try to give as much detail as possible. We live in Massachusetts, US. My wife is 5 months pregnant, and her employer already knew about it. She works at a consulate, but only as security. They’ve been discussing medical and family leave since it’s coming up soon obviously.

Here is the problem, today, out of nowhere, her boss told her that the client wants her to leave and work at another consulate nearby (they're in the same building). Apparently, the reason is—and I’m paraphrasing—because ‘she’s a softy with the customers and that’s risky for them,’ and also because ‘her being pregnant is too risky since people have been getting more aggressive lately.’

My wife was completely taken aback and super nervous. She couldn’t really speak up. Even her coworker from the other consulate was surprised and mentioned it might be too much for her. The other consulate is at least three times busier than hers, and the job would involve way more running around and using the elevator constantly. Plus, there’s been a lot more yelling and confrontations over there lately.

To make matters worse, the new position is not only more physically demanding as well as risky, but also pays less and has shifts that are an hour longer. Take in mind that my wife is very pregnant—she’s showing a lot, gets nauseous often, but still goes to work without complaining. We haven’t even asked for any accommodations, but this just feels like too much.

I’m at work right now and trying to calm her down as best I can, but we’re both really stressed. I told her to ask her boss to put everything in writing, but she’s already thinking about at least trying it for a week to see how it goes.

We’re also considering whether she should just go on medical leave and figure this out after the baby comes, but we really wanted to save that time for after the birth. Any legal advice? I read we can make a complaint but we are afraid we might need to get a lawyer. Do we wait or we need to start making the complaint right away?