The former Sopranos star, serving 10 years for his role in a burglary in New York that ended with the murder of an off-duty cop, was confined to his cell for 23 hours a day last year (11) after punching Alvaro Hernandez.
The incident, which was sparked by a disagreement about the use of a prison phone, is now the subject of legal action launched by Hernandez at Queens Supreme Court.
Hernandez is seeking damages for the injuries he alleges Brancato inflicted, according to the New York Post.
The former Sopranos star was sentenced to 10 years in January last year (10) for his role in a burglary that ended with the murder of an off-duty New York cop.
But Brancato Jr.'s time behind bars has become even harder to serve - he's only allowed out of his cell for one hour a day and has lost his phone privileges.
The punishment was handed down after the A Bronx Tale actor repeatedly punched another inmate during a bust-up in a communal area at Oneida Correctional Facility in New York, according to the New York Post.
The alleged victim, convicted thief Alvaro Hernandez, tells the publication, "He thinks he runs the place, like he's God's gift to this earth. He tells me, 'Hang up the phone, I gotta use the phone!' He forces open the door and spits at me, and he's punching me in the face and on the head."
After a probe by prison officials, Brancato was ordered to spend 23 hours a day in his cell and lose his right to use a phone. The punishment will last for one month.