Employer deducting bonus from outstanding pay?

I am located in Massachusetts. I began working for a small non-profit about 60 days ago. The job offer included a bonus split into two payments over 90 days. I have received one payment so far.

I don't believe this job is maintainable due to environment, unethical behavior on the part of management, etc. I am concerned about some fine print in my offer letter:

"Should you resign your position with [Employer] within the first ninety (90) days of employment, the full sum of this bonus will be deducted from any outstanding wages to the extent allowed by law."

To my understanding, they will subtract the bonus payment I was paid out from my remaining earned income if I resign within 90 days. This would remove more than my last two weeks of pay if I give two weeks notice.

I can't find any applicable law in my state (Massachusetts) via Google. Is this legal? Would I have any recourse if they tried to do this or is it better to try and stick out the remaining 30 days or let them fire me?

Thanks!