"Botched" star Dr. Terry Dubrow and "Real Housewives of Orange County" star Heather Dubrow are being sued for allegedly extorting a lawyer ... threatening to blast him on social media if he didn't make good on a business deal gone bad.
THE BACKSTORY: The Dubrows claim several years ago their accountant and the accountant's friend, attorney Steve Czik, came to the good doctor and his wife and said there was a woman who had a surefire business venture -- renting property for the World Cup, but she needed seed money.
The Dubrows claim the accountant and Czik convinced them to pony up $1.75 million, and they'd get a sweet return on that investment. The Dubrows say their accountant and Czik said it was such a no-brainer that they agreed to guarantee the loan.
Short story ... the woman never paid the Dubrows back, and they say their accountant and Czik refused to honor their guarantee. The Dubrows sued all 3.
THE ALLEGED EXTORTION: Cizik claims in a new lawsuit, Dr. Dubrow and Heather threatened him like a motha' ... pay up or they'd ruin him. Cizik claims he got an email warning, "Your photo will be published in every magazine and all over Instagram if you don't pay us," adding, "how f****** stupid are you?"
And the email went on, calling him a "lying scum sucking ass****."
He also boasted "TMZ Live" was going to cover the story.
Czik also claims harassment and defamation.