Two US musicians are suing Ed Sheeran for $20m (£13.8m) over his single Photograph.

Martin Harrington and American Thomas Leonard claim it has a similar structure to their song, Amazing.

The pair say that Sheeran's ballad has the same musical composition to their track, which was released by former X Factor winner Matt Cardle in 2012.

Martin Harrington and Thomas Leonard say they penned Amazing in 2009.

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

They say the similarities are "instantly recognisable to the ordinary observer".

These are the chord structures of the choruses in Photograph and Amazing compared in court documents.

The 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 film.

The copying of Amazing by Photograph is breathtaking in its deliberateness, magnitude, and hubris Court documents

The lawsuit says: "Given the striking similarity between the chorus of Amazing and Photograph, (the) defendants knew when writing, publishing, recording, releasing, and distributing Photograph that they were infringing on a pre-existing musical composition.

"The conduct of (the) defendants has been wilful from the inception of the creation of Photograph.

"The copying of Amazing by Photograph is breathtaking in its deliberateness, magnitude, and hubris."

Here's Ed Sheeran's track Photograph.

Warning: Third party content might contain ads

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

Here's that version of the track.

Warning: Third party content might contain ads

Documents in the copyright infringement case were filed on Wednesday 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 $20m (£13.8m), as well as royalties from the song.

Martin Harrington and Thomas Leonard are using the same lawyer, Richard Busch, who won a case for the family of the late soul singer Marvin Gaye.

He successfully sued Robin Thicke and Pharrell Williams for copyright infringement last year over their single Blurred Lines, winning a $7.4m (£5.1m) settlement.

Photograph was the fifth single from 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".

Ed Sheeran 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.

Peter Oxendale, who worked on Blurred Lines/Marvin Gaye case last year, said people in the music industry were "getting paranoid about infringing copyright".

The leading forensic musicologist told Newsbeat that the verdict had made the whole music industry "worried".

Ed Sheeran's management have not commented.

Matt Cardle has distanced himself from the case writing on Twitter.

Find us on Instagram at BBCNewsbeat and follow us on Snapchat, search for bbc_newsbeat