The investigation stems from alleged videos from a Kneecap gig where the rap trio apparently shouted, “Up Hamas, up Hezbollah.” Per the BBC, both militant groups are banned in the U.K. and expressing support for them is a crime.

In an open letter organised by Heavenly Recordings, Kneecap label, artists such as Massive Attack, Paul Weller and more say that “in a democracy, no political figures or political parties should have the right to dictate who does and does not play at music festivals or gigs that will be enjoyed by thousands of people.”

British counterterrorism detectives will investigate comments by Irish hip-hop group Kneecap, which has been criticized by U.K. politicians over statements about the Middle East and British politics,