The letter, obtained by Sports Illustrated's The Crossover, includes Rubin's impassioned plea to Judge Genece E. Brinkley before Mill's sentencing.
Rubin will also attended a Monday rally for the rapper which calls for justice for Meek and others. "We stand for justice", along with hashtags #justice4meek and #freemeekmill.
Many in the crowd chanted "Free Meek Mill" and sang the rapper's "Dreams and Nightmares" intro together.at the rally, which was planned to begin in front of Philadelphia's Criminal Justice Center at 5 p.m.
Mill, who had been on probation for a decade, was arrested in March after he got into a fight in St. Louis.
Another woman accuses George HW Bush of groping her
The former president served as CIA director in the 1970s, and the agency's headquarters in Langley, Va., is named for him. The incidents have also raised questions about the role of his family in preventing such contacts from occurring.
The co-owner of the Philadelphia 76ers, Mark Rubin, has also thrown his support behind Mill.
In August, he was charged in NY for popping wheelies on a dirt bike and failing to wear a helmet.
Mill's lawyer Joe Tacopina has charged that Brinkley was romantically drawn to Mill's celebrity status, and felt rebuffed by the rapper. The judge also reportedly made a request that Meek should re-record Boyz II Men's song "On Bended Knee" which he tributes to her and mentions her by name in the song. I explained to her that I recognized Meek did some dumb things in the past and was working hard to make things right. He took a plea for the charge in NYC and the airport assault was was dropped, but it was still enough for the judge in Philly to violated Williams and sit him behind bars for what many say was an overzealous sentence.
Kaerpernick joins Jay-Z and Rick Ross in speaking out about Mill's sentence. I'm asking for mercy.