The heirs of songwriter Ed Townsend have sued Sheeran in New York federal court for copyright infringement of the 1973 soul hit "Let's Get It On." Townsend and Marvin Gaye co-wrote the song.
"The Defendants copied the 'heart' of 'Let's' and repeated it continuously throughout 'Thinking,'" the lawsuit claims. It alleges there are "melodic, harmonic, and rhythmic compositions" in the two songs that are "substantially and/or strikingly similar."
Gaye died in 1984 and Townsend died in 2003.
The suit names Sheeran, "Thinking Out Loud" co-writer Amy Wadge, music producer Jake Gosling, Sony/ATV Music Publishing, Atlantic Records, Asylum Records, and Warner Music Group as defendants.
CNN has reached out to representatives for Sheeran and his record label for comment.
Sheeran is also battling another copyright lawsuit. In June, songwriters Martin Harrington and Thomas Leonard filed suit in Los Angeles federal court accusing Sheeran of stealing from their song "Amazing" on his song "Photograph."
The pair are seeking $20 million in damages.
Last year, Gaye's family successfully sued singer Robin Thicke and producer Pharrell Williams for $7.4 million for borrowing from Gaye's "Got to Give It Up" for their hit "Blurred Lines."