We're told 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.
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.
As we previously reported, Kelis' rapper ex-husband Nas has been ordered to pay her over $25,000 a month in child and spousal support. Not too shabby.
Calls to Kelis' camp haven't been returned.