Lizzo has been accused of failing to give a credit to two songwriters who claim they helped come up with a famous lyric in her hit Truth Hurts.
Justin and Jeremiah Raisen say the line "I just took a DNA test turns out I'm 100% that..." came from a writing session which they were a part of.
They claim they've been trying to sort out the issue for two years but have been "shutdown" every time.
Lizzo's lawyer, Cynthia S Arato, has denied their claim.
In a post on Instagram, Justin and Jeremiah said they wrote a song called Healthy with Lizzo and two other writers at their studio in April 2017.
They say the line "I just took a DNA test turns out I'm 100% that..." was taken from that song and used in Truth Hurts.
The brothers say they were never contacted about being credited for the use of parts of Healthy and have been trying to sort it out "quietly" for the last two years.
They claim they were asking for 5% each but were "shutdown every time".
"Coming forward publicly to family, friends, artists, and colleagues seems to be the only way at this point in relieving some of our emotional distress caused by this," they wrote.
"The last thing we want to do is throw any negativity toward Lizzo's momentum and movement as a cultural figure.
"If we believe in what she's preaching, believing in ourselves and our own voices it's something we thought she'd understand."
Producer Ricky Reed is credited on Truth Hurts along with Lizzo
Their post included a video which they say shows a video and photos from the day they wrote Healthy as well as a comparison between the two songs.
Truth Hurts was originally released in America in 2017 but went to number one in the US charts earlier this year.
The line "I just took a DNA test turns out I'm 100% that..." has been used loads on social media - including by former US Secretary of State Hillary Clinton.
The song's credits list four writers - Lizzo, producers Ricky Reed and Tele, and singer-songwriter Jesse Saint John.
This isn't the first time there's been controversy over the lyric.
In February 2017, British singer Mina Lioness tweeted the exact same line - which has received thousands of likes.
When news that Lizzo wanted to trademark the lyric emerged in June 2019, she was accused by some of stealing it from Mina.
It's something she denied.
Mina even tweeted Lizzo, saying: "Now everyone believes those were your words, when in fact they were mine. My creativity, my wit and my comedy."
The singer replied saying that she had never seen Mina's viral tweet but was "glad it exists".
In their Instagram post, Justin and Jeremiah referenced Mina - saying a meme of the line she tweeted out came up in their writing session and "inspired the lyric and melody" of Healthy.
They added: "If Ricky and Lizzo's team decide to settle this dispute with us, we would like to share some of the proceeds with Mina for her influence on Healthy."
In a statement to the New York Times, Lizzo's lawyer Cynthia S Arato denied the brothers' claim.
"The Raisens are not writers of Truth Hurts.
"They did not collaborate with Lizzo or anyone else to create this song, and they did not help write any of the material that they now seek to profit from, which is why they expressly renounced any claim to the work, in writing, months ago."