Mariah Carey works her hired help to the bone, and then kicks 'em to the curb when she's had enough ... so claims her ex-nanny in new legal docs.

MiMi's being sued by a woman named Maria Burgues, who claims she worked for Mariah between late 2017 and early 2018 ... watching over her two kids and, allegedly, flying all over the world with them without getting paid her fair share for the job she was doing.

Burgues alleges in her lawsuit -- obtained by TMZ -- that Mariah and co. wouldn't let her take required breaks she's supposed to get under California law, including rests and meals. Burgues says those just weren't a thing while she was employed.

Burgues doesn't get specific about what exactly her schedule or allotted hours for each week were, but she makes it sound like she was working round the clock for Mariah, often on non-nannying duties and tasks that allegedly didn't involve the kids at all.

Adding insult to injury, Burgues claims Mariah had a bodyguard she reported to who was a scumbag and allegedly treated her like dirt out in the open on more than one occasion. She even alleges the guy almost got them into a major traffic accident for being on his phone.

She also alleges the guy once threatened to boot her from the car on a drive to Vegas. The nanny says when she finally complained, she was fired shortly thereafter ... and seems pretty sour about it.

Moreover, she claims Mariah didn't keep proper track of her hours -- and she believes they owe her unpaid wages on her then-$25/hour salary ... plus damages, of course.

We reached out to Mariah ... so far, no word back.