Jessie J is being sued by a US artist who claims her hit Domino is a copy of one of his songs.
Will Loomis has compared Jessie's chart-topping song to his 2008 track Bright Red Chords, by his band Loomis & the Lusts.
He wrote on his Facebook page: "When I wrote this melody in my garage I never imagined it would be sung for the King and Queen of England. I especially never imagined it would be sung by Jessie J."
The Voice star performed her track Domino at the Queen's Diamond Jubilee concert earlier this month.
Will's lawyer said in a statement to Billboard magazine: "Loomis never consented to the use of his song. We look forward to obtaining an appropriate remedy from the court for this clear infringement."
The lawsuit cites Jessie herself and her labels Universal Music Group, Lava Records and Universal Republic Records.
A spokesperson for Jessie, 24, has not yet commented.
She wrote Domino with Lukasz Gottwald (also known as Dr Luke), Kelly Claude, Martin Sandberg and Henry Walter, and scored her second UK Number One when it was released last December.