The "Jealous" singer reveals Mayer approached the trio years ago and confessed he was a big fan of their song "Lovebug" - and then went off and revamped the tune.
Appearing on a new episode of YouTube series "Hot Ones", Nick said, "He did kinda copy a song of ours. Little known fact. Look it up on YouTube."
"He came to us at the Grammys years ago and he said, 'I love your song Lovebug...' Two years later he released a song and the chorus is literally the same with different lyrics."
But Mayer needn't worry about a plagiarism bid, as Nick insists, "It's a compliment when somebody does that!"
The Mayer song in question is "Walt Grace's Submarine Test", January 1967, which featured on his 2012 album "Born and Raised".