Christopher Plummer and Frank Langella have joined HBO Films' Muhammad Ali's Greatest Fight. The project is being directed by Stephen Frears.

The film follows the legal fight between Ali and the U.S. government when the fighter became a conscientious objector to the Vietnam War. Mohammed Ali was drafted into the Army in 1966 but declined to serve, citing his belief that the war was against the teachings of the Koran. When he appeared at an armed services induction in 1967 and refused to step forward when his name was called, he was arrested.

Shawn Slovo will be writing the script with Frank Doelger, Tracey Scoffield and Jonathan Cameron producing.

No production date has been set.