*A housekeeper working for Kelis claims the R&B singer owes her $900 in unpaid wages – but she’s having a problem seeking repayment through the courts because of her undocumented status.

According to TMZ, Kelis’ 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.

Sources say the housekeeper is currently exploring her legal options — trying to obtain a lawyer to see if she can pursue justice through the California Labor Commission.

Meanwhie, Kelis’ rapper ex-husband Nas has been ordered to pay her over $25,000 a month in child and spousal support.