'Three Stooges' -- You Can't Jack Our Comedy With Porn!

The brainchild behind the porn parody, "Not the Three Stooges XXX" has been threatened by the guy behind the PG version that was released Friday -- to either put the brakes on the porn, or else.

Robert Benjamin, Executive VP and General Counsel of C3 Entertainment which produced the PG movie, fired off a letter -- obtained by TMZ -- to the lawyer for the triple X version, claiming the "low budget, clearly pornographic film" is not protected as a parody under the First Amendment.

But Michael Fattorosi, the XXX lawyer fired his own letter back -- which we also got -- claiming the only way Benjamin could stop him is with a proper trademark, and Fattorosi says the only Three Stooges trademark Benjamin owns is for Three Stooges bottled beer.

But even more basic -- Fattorosi lectures Benjamin on the fact that a parody is protected as free speech.

The PG movie came in second last weekend, pulling in $17 mil.