Porn King to MTV -- Farrah Abraham Sex Tape Is Coming ... Speak Now, Or Forever Hold Your Peace

The porn honcho behind the release of "Teen Mom" Farrah Abraham's sex tape is giving MTV -- which carries the show -- fair warning ... the video will be released to the world on Monday ... unless they come up with a really good legal reason to keep it under wraps.

Vivid Entertainment Prez Steve Hirsch is downright diabolical ... sending the network a "put-up-or-shut-up" ultimatum just days before the tape goes wide. Hirsch wants to know if there's something in Farrah's contract that would prohibit her from doing her backdoor tricks with porn star James Deen.

So the clock -- we said clock -- is ticking as the world waits to watch Farrah take a licking.