Carly Rae Jepsen is cancelling her performance at the Boy Scouts of America Jamboree because of the scouts' exclusion of gay members.
The Call Me Maybe singer said on Twitter that "as an artist who believes in equality for all people" she's pulling out of the July gathering in West Virginia. The event, held once every four years, is expected to draw more than 45,000.
Rock band Train also warned that it won't appear unless the organisation stops barring participation by gay scouts or adult leaders.
Train said on its website that it was unaware of the policy before agreeing to perform and that the organisation must now make "the right decision".
BSA director of publicity Deron Smith said the BSA appreciates "everyone's right to express an opinion" and remains focused on staging a great jamboree.