Carmelo Anthony is calling on fellow athletes to start using their fame for political purposes in the wake of two high-profile killings of black men and the gunning down of five police officers this week.

“I’m calling for all my fellow athletes to step up and take charge,” the 32-year-old New York Knicks star posted to his Instagram account alongside a photograph of Muhammad Ali, Jim Brown, Lew Alcindor and other black athletes at a 1967 meeting pertaining to Ali’s status as a conscientious objector. “There’s no more sitting back and being afraid of tackling and addressing political issues anymore. Those days are long gone. We have to step up and take charge. We can’t worry about what endorsements we gonna lose or whose [sic] going to look at us crazy. I need your voices to be heard. We can demand change. We just have to be willing to.”

The nine-time all-star, who attended a #BlackLivesMatter protest in Baltimore last year, strongly condemned the shootings in Dallas that disrupted an otherwise peaceful protest on Thursday about the deaths of Alton Sterling and Philando Castile, but said it’ll take more than tweets and marches for athletes and others to “change the system.”

“Shooting 11 cops and killing 5 WILL NOT work,” he wrote, noting there was no easy formula ahead.

“We have to be smart about what we are doing,” he wrote. “We need to steer our anger in the right direction. The system is Broken. Point blank period. It has been this way forever. Martin Luther King marched. Malcolm X rebelled. Muhammad Ali literally fought for US. Our anger should be towards the system. If the system doesn’t change we will continue to turn on the TVs and see the same thing.”

The power of Anthony’s words did not go lost on The New York Daily News, which published his comments in their entirety on the back page of its Saturday edition.

Preemptively answering Anthony’s calls to step up is LeBron James, who posted a spate of tweets late Thursday night and early Friday morning calling for the violence to stop .

Like Anthony, James has used his celebrity to bring attention to the #BlackLivesMatter movement in the past. Most prominently, he joined a handful of other athletes in 2014 by wearing an “I can’t breathe” shirt to warm up before a game in response to a Staten Island grand jury’s decision not to indict the police officer who placed a deadly chokehold on Eric Garner.

James’s words then echo his words now.

“This is our country, the land of the free, and we keep having these incidents happen, innocent victims or whatever the case may be,” James said (via Cleveland.com) in 2014. “It’s a sensitive subject right now. Violence is not the answer and retaliation isn’t the solution. … As a society we just have to do better.”