Songwriters Martin Harrington and Thomas Leonard are suing Ed Sheeran for $20 million over his single Photograph.

The California-based musicians claim the track has a similar structure to one of their songs.

They allege Ed Sheeran’s ballad, released as a single in 2015, has the same musical composition to their song Amazing.

Martin Harrington and Thomas Leonard say they wrote their track in 2009.

In court documents, that include musical note comparison and chord breakdowns of the two songs, the musicians claim the chorus of Photograph shares 39 identical notes with Amazing.

They say the similarities are “instantly recognizable to the ordinary observer”.

The court documents say that Photograph has sold more than 3.5 million copies worldwide.

It says it also features prominently in Hollywood drama Me Before You, released last week, as well as trailers for the movie.

Martin Harrington and Thomas Leonard’s song Amazing was adapted into a single of the same name for Matt Cardle, the winner of The X Factor in 2010.

Matt Cardle’s version of the track has more than one million views on YouTube, while Ed Sheeran’s music video for Photograph has 208 million.

Documents in the copyright infringement case were filed on June 8 at LA’s federal court in the Central District of California.

Other named defendants being sued include Snow Patrol’s Johnny McDaid, who is credited as a co-writer on Photograph, as well as various divisions of Sony/ATV Music Publishing, Warner Music Group and its subsidiary, Atlantic Recording Corporation.

Martin Harrington and Thomas Leonard, and their publishing company HaloSongs, want a trial and damages of more than $20 million, as well as royalties from the song.

They are using the same lawyers who won a case for the family of the late soul singer Marvin Gaye.

They successfully sued Robin Thicke and Pharrell Williams for copyright infringement last year over their single Blurred Lines, winning a $7.4 million settlement.

Photograph was the fifth single from Ed Sheeran’s 2014 album x (pronounced multiply).

The court documents say Ed Sheeran had called the song “the one that will change (his), kind of, career path”.

The singer has written and co-written tracks for artists like One Direction, Taylor Swift and Justin Bieber.

British songwriter Martin Harrington has written tracks for Emma Bunton (What Took You So Long), 5ive (Let’s Dance) and Kylie Minogue (Love at First Sight) as well as working with Stevie Wonder, Celine Dion, Westlife, Busted, Atomic Kitten and Blue.

Thomas Leonard’s writing credits include Safe Place to Hide by Backstreet Boys as well as songs by Zero 7 and Echosmith.