A prison officer faces punishment for showing the gay cowboy movie "Brokeback Mountain" to inmates at the state's largest prison, a corrections department spokeswoman said.

Massachusetts Department of Correction spokeswoman Diane Wiffin said the officer, whose name was not released, had not followed standard procedure for screening the movie for excessive violence, assaults on correctional staff, nudity or explicit sexual content.

She would not reveal what discipline the officer could face.

"I want to make it clear, it wasn't the subject matter — it was the graphic nature of the sexually explicit scenes," Wiffin said Monday.

The officer showed the movie Thursday at MCI-Norfolk, a medium security prison about 25 miles southwest of Boston. According to Wiffin, a deputy supervisor came in as the movie was showing and asked if the officer had screened it first. He said no. Since only 20 minutes remained of the movie, the inmates were allowed to see the end, she said.

Wiffin did not know how many inmates saw the movie and did not know of any other instance when a prison officer was disciplined over a movie.