Catherine Grieg, 64, was indicted by a federal grand jury in Massachusetts on one count of criminal contempt. She has refused to testify before a grand jury since December 2014, prosecutors said.
Grieg, who's serving an eight-year sentence for conspiracy to harbor a fugitive, identity fraud and conspiracy to commit identity fraud, could face more prison time if convicted.
"Catherine Greig has yet again failed to do the right thing," said Joseph Bonavolonta, acting special agent in charge of the FBI's Boston division. "Her refusal to testify has hindered the FBI's efforts to seek justice for the victims of his crimes."
The indictment comes less than a week after “Black Mass,” a movie about Bulger’s life starring Johnny Depp, was released in theaters.
Grieg was found living with Bulger -- whom her lawyer called "the love of her life" -- in a Santa Monica, Calif., apartment in 2011. The pair had been on the run since 1994 and outfitted the rent-controlled home with holes in the walls to hide 30 weapons and $800,000 in cash.
James "Whitey" Bulger is pictured shortly before he disappeared in 1995.
James "Whitey" Bulger, was convicted in a Boston federal court in August 2013 on a broad indictment that included racketeering charges in a string of murders in the 1970s and '80s.
The lovebirds posed as a married retired couple from Chicago, using false identities to make doctor appointments and pick up prescriptions, prosecutors said.
Grieg agreed to plead guilty during her trial in 2012 so she wouldn't have to testify against her man, who is now serving a life sentence in connection to 11 murders.
She wasn't always by Bulger's side though.
The mob boss initially ran off with his longtime beau Teresa Stanley, who he'd dated since the 1960s as he was seeing Grieg, the FBI said. Two months later, Bulger returned to Boston to drop off Stanley and pick up Grieg.
Bulger, who served as an FBI informant, has not yet seen the movie based off his life, his attorney said earlier this week of the 86-year-old.
“I think it’d probably be unlikely for him to see it, because he’s incarcerated and they have no cable," attorney Hank Brennan said.