The production is currently onstage at the Royal Opera House in London and the late star's former boyfriend, Larry Birkhead, has revealed lawyers are drawing up legal documents.
He claims the producers never contacted Anna's estate bosses or him about the opera, which he calls a "sleazy tabloid".
Birkhead tells TMZ.com, "If they (producers) are not careful, they'll get more than diet pills in the mail."
The new opera features an explicit scene in which the star performs oral sex on her late wheelchair-bound husband, 80-year-old oil tycoon J. Howard Marshall.
Composer Richard Thomas has previously defended his decision to create the show, insisting Smith's tragic life was "endlessly fascinating and perfect" for the stage.