Fortress Investment Group LLC filed suit against Ruskin Moscou Faltischek on Tuesday for allegedly issuing “utterly false” legal opinion letters used by ex-lawyer Marc S. Dreier, who is now in prison for his role in a massive Ponzi scheme.

In a complaint filed in Manhattan Supreme Court, Fortress claims the Uniondale, N.Y.-based law firm issued three letters that Dreier used to defraud the investment firm out of $50 million. The suit against Ruskin Moscou follows one filed by Fortress in December against Dechert that made similar allegations.