With a month-to-month lease, the landlord can ask the tenant to leave for any reason (other than discrimination) provided they give the tenant 30 days notice.
Summer YCombinator teams take note: Mass is also a right-to-rent state. If you don't have a formal, set-term lease (a verbal contract, month-to-month, or expired lease) both the tenant and landlord can call it quits with a 30 day notice with no reason required. Very handy if you ask me. If you want a formal lease you can find one but if you and the landlord are OK with a looser arrangement that is OK too.