(CNN) - Amid mounting backlash over rapper Meek Mill's prison sentence, hundreds of activists and prominent personalities -- including Rick Ross, the Philadelphia Eagles' Malcolm Jenkins and the Philadelphia 76ers' Julius Erving -- gathered at Philadelphia's Criminal Justice Center on Monday for a rally protesting the rapper's imprisonment.
"(Meek)'s obviously despondent about his plight, so to speak, but also is encouraged by all the support," Mill's attorney, Joe Tacopina, told CNN in a phone interview Monday night. "This is overwhelming to me, all the people who have come rallying behind him."
Pennsylvania Gov. Tom Wolf's office told CNN that the governor's hands are tied because he is "not able under PA law of intervening" in a specific case, as it was suggested in a Change.org petition.
The petition, which has been signed by more than 351,000 supporters of Mill by Monday night, initially called for Wolf to re-evaluate the Philadelphia rapper's two- to four-year prison sentence. The petition has since been revised and addressed to the state's Board of Pardons as well as Wolf.
"The pardon process in Pennsylvania is different than some other states and the federal government," Wolf's press secretary, J.J. Abbott, told CNN in an email Monday, alluding to the fact that in other states, a governor can evaluate cases without the involvement of a board.
This case has sparked outrage not just from the hip-hop community but from activists for criminal justice reform around the nation, including Colin Kaeperinck.
The former San Francisco 49ers quarterback became a symbol of resistance against racial bias in policing after he took a knee during the National Anthem last year to protest police brutality.
"Sadly there are Black folks going through the same radicalized injustice(s) within the justice system that Meek Mill has experienced for over a decade EVERY SINGLE DAY. This requires more than just gradual reform in laws—It requires a swift overhaul," Kaepernick tweeted on Monday.
In a show of support and encouragement for Mill, a crowd of fans rapped one of his most popular songs, "Dreams and Nightmares," at the rally. The single was released in 2012, and in it, the rapper reflects on growing up in poverty, his initial incarceration in 2008 and how he overcame his struggles -- going from handcuffs wrapped around his wrists to a Rolex watch.
Mill appeared in court last Monday after a pair of arrests this year -- one for popping wheelies on a dirt bike and another for getting into a fight -- that violated his probation from a 2008 gun and drug case. He was sentenced to another five months in prison in 2014 after he violated his probation by performing out of state.
He received to two to four years in state prison last week by Judge Genece Brinkley, who cited a failed drug test and the rapper's noncompliance with a court order restricting his travel.
Tacopina accused Brinkley of "taking an inappropriate personal interest in (Meek Mill) that goes above and beyond her role as a judge."
"(Meek's) frustrated, really frustrated, and knows he's being treated different than anyone else," Tacopina said.
"He's been on probation for nearly 10 years. Nobody goes on probation for 10 years," he added.
Brinkley's office did not respond to a request for comment and instead referred CNN's request to Gabriel Roberts, a spokesman for the 1st Judicial District of Pennsylvania, which declined to comment as the matter is "subject to future litigation."
Supporters of Mill, including Jay Z, argued that the sentence was too harsh and should not have included incarceration.
Read more about the controversy and Mill's background with the judge.
Tacopina told CNN on Monday that he plans to exhaust all legal avenues as well as political avenues to remedy what he called "an obvious injustice."
In the next couple of days, Tacopina said he plans to make a motion for Brinkley to "recuse" herself from the case and then file a motion for her to reconsider the sentence.
Asked what his plan is if both motions fail, Tacopina said he would then "go the appellate route" and file a formal appeal.
Another way forward is filing an application for the state's Board of Pardons, a political avenue that Tacopina said they also plan to pursue.
Mill is signed to Jay Z's record label Roc Nation, which urged fans to sign the Change.org petition addressed to the board and Wolf.
"The sentence handed down by the judge -- against the recommendation of the assistant district attorney and probation officer -- is unjust and heavy-handed," Jay Z said in a statement provided to CNN. "We will always stand by and support Meek Mill, both as he attempts to right this wrongful sentence and then in returning to his musical career."