Instagram warns Rihanna says her account might permanently be shut down

Instagram warns Rihhana, says her displays of public nudity go way too far and is now threatening the singer within an inch of her exposed nipples.

Rihanna posted topless snaps Tuesday from her photo shoot with Lui, a French skin mag -- and within an hour IG yanked 'em down ... because they violated rules against nudity.

A source says Rihanna got an email that basically warned her ... keep your clothes on or risk having your account permanently shut down.

But like a bikini trying to contain her boobs -- IG couldn't stop RiRi ... and she just posted the banned nudes on Twitter instead.