Insane Clown Posse is suing the US Justice Department and the FBI, for classifying their loyal fans – the "Juggalos" – as members of a criminal gang, the New York Times has reported.

In a suit filed on Wednesday, the Michigan rap duo claimed the decision to classify the Juggalos as a gang was "unwarranted and unlawful" and had led to fans being harrassed. Four fans – from Nevada, California, North Carolina and Iowa – have joined ICP founders Joseph Bruce and Joseph Utsler and the Michigan branch of the American Civil Liberties Union in the suit.

The four fans said in the complaint that they had been subject to police harrassment or punishment because of their association with the band. Mark Parsons, from Nevada, said he was detained by Tennessee state troopers for displaying an ICP insignia on his truck. Scott Gandy, from North Carolina, said he had spent hundreds of dollars having Juggalo tattoos covered with other tattoos after being told he could not join the army with "gang-related" body art.

The two band members said one of their concerts in Michigan had been cancelled after local police had "cited the federal Juggalo gang designation".

The gang designation had its roots, the NYT reported, in a 2011 report from the FBI's National Gang Intelligence Center, which described the Juggalos as a "loosely organised hybrid gang", and cited two incidents in which "suspected Juggalo associates" or members were involved in violent crime.

In the lawsuit, ICP say their music is actually laden with "hopeful, life-affirming themes about the wonders of life and the support that Juggalos give to one another".

The Juggalos are one of rock's most zealous fanbases – so much so that Whoop Dreams, a documentary about fans at the band's annual Gathering of the Juggalos, is set to be released this year.

Reading on mobile? Watch the Whoop Dreams trailer here