The two friends have been spotted protesting on the streets of Los Angeles in recent days and now they've hooked up to collaborate for a good cause.
"They (Rage Against the Machine) wrote this song in 1992. It's been 28 years since, and every word still applies," Kelly wrote on Twitter. "Me and Travis Barker wanted to bring it back for these times...".
The accompanying video features black and white footage of Barker and Kelly protesting, with the rap-rocker holding a sign that reads: "Stop arresting protestors! Arrest Killer Cops".