Kelis’ housekeeper claims she is owed $900 in unpaid wages — and according to sources, there’s one major problem preventing her from seeking justice … she’s an illegal alien.

The maid earned $150 a day for her work … and since she only worked one day a week, that means Kelis somehow fell six weeks behind on her payments.

According to sources, the housekeeper is currently exploring her legal options — trying to lock down a lawyer to see if she can file anything with the California Labor Commission.