Farrah Abraham -- Vivid Tried to Backdoor Me on Sequel

Farrah Abraham insists she did NOT consent to a second sex tape which is about to be marketed ... claiming her initial tape was a one off and she is NOT a porn star.

Farrah's lawyer tells TMZ ... his client did not give Vivid honcho Steve Hirsch permission to release a sequel to "Backdoor Teen Mom." The lawyer says the so-called new sex tape is just extra footage from the first shoot she did -- with porn star James Deen.

According to the lawyer, Farrah is "a mother, a public figure, and an author," and not a porn star.

The lawyer says they tried to shut down Hirsch, to no avail.

Something tells us ... Hirsch has a release (not that kind) in his hands that gives him the right to the footage.