I'LL SUE ... IF MY SEX TAPE WITH TYGA LEAKS!!! - BLAC CHYNA

Someone's shopping around what they say is a Blac Chyna/Tyga sex tape, and the leading lady is doing everything within her power to keep it in the can. 

Blac Chyna's lawyer, Walter Mosley, tells TMZ Chyna will go after anyone who releases the tape ... with a vengeance.  

A tape has been sent to media outlets and porn companies ... we can't vouch for the identity of the stars, but the tattoos match.

As far as we know, so far there are no takers.