"EMPLOYMENT AT WILL"
“Employment at will” is the default rule in Massachusetts (and in almost every other state in the U.S.). That means that unless you are covered by a union contract (collective bargaining agreement) or some other contract that gives you job protections, you are probably employed “at will.”
This means that as a general rule, employers may hire and fire as they please, and by extension, treat their workforces as they see fit. (Some government workers have additional protections. And even if your employer is allowed to fire you, you still might be eligible for unemployment benefits.)
Employers do not always have to treat workers fairly, even if it causes harm.
BUT there are many exceptions to this general employment-at-will rule. The key is to find an exception that fits your situation, such as discrimination.
UNLAWFUL DISCRIMINATION
A covered employer may not treat you differently and worse because of your race; color; age (if you are over 40); sex; pregnancy; national origin; ancestry; religion; disability; genetics; sexual orientation; or gender identity or expression.
A covered employer may not retaliate against you because you complained of unlawful discrimination or exercised your rights under the discrimination laws (for example, by requesting a disability accommodation).
With some exceptions, covered employers may not ask applicants or employees to furnish certain criminal information, and may not take an adverse employment action against an applicant or employee because of criminal history information the employer has obtained unlawfully.
Discriminatory harassment is also unlawful.
More information about pursuing a claim of discrimination.