Kanye West, who is demanding to be released from his recording and publishing deals, has uploaded photos of his contracts to Twitter.
"I need every lawyer in the world to look at these," he told his followers, while referring to the music industry as "modern-day slavery".
Taking aim at the wider music industry, he later posted a video of someone urinating on a Grammy award.
West says he won't release new music until he is released from his deals.
The cache of documents he posted on Wednesday night included details of advance payments for his albums, royalty rates, a profit sharing agreement, and several amendments.
Some are only partially complete, and their validity has not been corroborated - but they appear to show that West was given a $12m (£9.2m) advance for his sixth album, Yeezus, and receives royalties of between 14% and 25% on his sales and streams.
According to music industry lawyer Aurelia Butler-Ball, such multi-million-dollar advance payments are "rare in today's industry, because the money just isn't there". However, West's royalty rates are typical of the deals she sees for her clients.
"If the label is going to take the risk and give that upfront investment, then they want the majority of the income when the record is sold," she told the BBC.
"A very high-profile, well-established artist can sometimes negotiate slightly higher royalty rates, but that's really just the industry standard."
Butler-Ball, who is a senior associate at Irwin Mitchell, said it was "difficult to pinpoint" West's aim in revealing his densely-worded contracts, but it appeared that his relationship with the label was irreparably damaged.
"Ultimately, the success of a record deal isn't necessarily how good the contract is. It's about the strong relationship between the artist and the [people] at the record label.
"And once that relationship has broken down, which it looks like here, it's very hard to have success with each other, and make good music together, no matter what the contract says."
Universal have yet to respond to West's statements.
'I'm fighting for us'
The dispute comes a year and a half after the rapper sued EMI Publishing, seeking to terminate what he called a "lopsided and oppressive" contract that prohibited him from retiring.
EMI counter-sued West for damages in March 2019, after what it called "West's efforts to renege on his bargained-for contractual obligations to the company."
They reached an undisclosed settlement last September, in which it is likely that West renegotiated his terms and royalty rates.
On Monday, the star took a break from his faltering Presidential campaign to post a string of statements about his music career.
He began by announcing he was "not putting no more music out til I'm done with my contract with Sony and Universal".
West continued by demanding apologies "immediately" from fellow musicians J Cole and Drake, adding: "I'm fighting for us" and "I'm not gonna watch my people be enslaved".
The implication seemed to be that he wanted to form an alliance of artists who could combat unfair recording contracts. He later implored Bono, Kendrick Lamar "and even Taylor" Swift to join the cause, adding: "All the musicians will be free".
At the centre of his dispute appears to be an attempt to buy back the master tapes for his recordings.
"When you sign a music deal you sign away your rights," he posted. "Without the masters you can't do anything with your own music. Someone else controls where it's played and when it's played. Artists have nothing accept the fame, touring and merch[andise]".
"In COVID artist need our masters... it's more important than ever before".
When you sign a music deal you sign away your rights. Without the masters you can’t do anything with your own music. Someone else controls where it’s played and when it’s played. Artists have nothing accept the fame, touring and merch— ye (@kanyewest) September 16, 2020
On Tuesday, West claimed that Universal Music "won't tell me what my masters cost because they know I can afford to buy them".
He also tweeted texts from an unnamed adviser, who presented options for getting out of his contracts, and estimated the cost of his masters at more than $300m (£232m).
No one from Universal or Sony has responded so it’s Go time pic.twitter.com/k5K0c1t4eF— ye (@kanyewest) September 15, 2020
The 43-year-old later called out several senior executives at Universal by name.
Writing in capitals, he added: "Please understand that I will do everything in my legal power and use my voice until all artist contracts are changed. I will not stop. I promise you I am petty and very personal".
EVERYONE AT UNIVERSAL AND VIVENDI PLEASE UNDERSTAND THAT I WILL DO EVERYTHING IN MY LEGAL POWER AND USE MY VOICE UNTIL ALL ARTIST CONTRACTS ARE CHANGED STARTING WITH GETTING MY MASTERS FOR MY CHILDREN I WILL NOT STOP I PROMISE YOU IM AM PETTY AND VERY PERSONAL— ye (@kanyewest) September 16, 2020
West also highlighted that record contracts often contain "hidden costs" - which force an artist to pay for the distribution of their CDs, amongst other things.
Butler-Ball said that forcing labels to be more upfront about these fees "could only be a good thing".
"If he forces the hand for more transparency, in terms of where those costs are going, the days of artists having to cover the cost of printing 10,000 vinyl are over," she said.
'Vile and disrespectful'
West's Twitter account was later suspended after he posted the private phone number of Forbes' chief content officer Randall Lane, writing, "If anyone wants to call a white supremacist … this is the editor of Forbes."
Twitter was said to have frozen the account until he removed the post and agreed not to commit further violations of privacy.
The video of his Grammy award, lodged in a toilet and apparently being urinated upon, remains on the site.
It was criticised by hit songwriter Diane Warren, who called it "vile and disrespectful".
"This was given to you by your peers out of respect for your work and you are literally pissing on them," she wrote. "I've won one Grammy and I'm forever grateful and humble that my peers found me worthy of it."
Billie Eilish's brother, Finneas O'Connell, simply responded: "This is so sad, man".