Producer Lukas Burton filed the complaint stating he worked with Blunt early in his career but was dumped when the performer hit the big time, the BBC reported Saturday.
The six songs involved in the action were not named, but a PRS spokesman said Blunt's No. 1 "You're Beautiful" was not one of them.
The Blunt camp appeared confident the star would be vindicated.
"Traditionally, when a record is this massive, everyone wants to claim credit for its success," Blunt's spokeswoman told the BBC. "This is no different."