In Massachusetts landlords cannot legally charge you a late fee unless your rent is more than 30 days past due. Landlords will sometimes charge you a extra fee if your rent is not paid by the 10th of the month. This is illegal in Massachusetts and you can get your money back if you have paid this fee !
If your landlord has a lease/rental agreement that charges you a late fee before 30 days contact my office. Even if he hasn't tried to enforce the fee, its illegal and you could be entitled to compensation.
If you're a landlord - call my office and I can help you though the maze you need to follow to protect yourself from any potential pitfalls.