Taylor Swift has said she is "sad" and "grossed out" after entrepreneur Scooter Braun gained control of all her music - accusing the 38-year-old of "incessant, manipulative bullying".
Braun, who manages Justin Bieber and Ariana Grande, owns Ithaca Holdings, which bought Big Machine Label Group at the weekend, giving the entrepreneur ownership of her back catalogue.
Swift signed for Big Machine, founded by former Universal executive Scott Borchetta, in 2005 and moved to Universal Music Group in November last year.
In a post on Tumblr, Swift also claimed she was given no notice of the sale.
Writing on the site, she said: "I learned about Scooter Braun's purchase of my masters as it was announced to the world.
"All I could think about was the incessant, manipulative bullying I've received at his hands for years."
In response, Braun's wife, Yael Braun, came to his defence saying he is "anything but a bully", adding: "Interesting that the man you're so 'grossed out' by believed in you more than you believe in yourself."
Swift's post was also accompanied by a screen grab of an old social media post showing Braun with Justin Bieber and Kanye West - both of who he manages - with the caption: "Taylor Swift what up".
In her post, Swift, whose new album Lover is released in August, continued: "I am now signed to a label that believes I should own anything I create.
"Thankfully, I left my past in Scott's (Borchetta, founder of Big Machine) hands and not my future.
"And hopefully, young artists or kids with musical dreams will read this and learn about how to better protect themselves in a negotiation.
"You deserve to own the art you make."
In response, Borchetta said he wanted to "set things straight" in a post entitled "So, It's Time For Some Truth" on Big Machine's website.
He wrote that Swift's father Scott Swift was a shareholder in Big Machine and was alerted about the pending deal on June 25.
He added: "We then had a final call on Friday, June 28th in which the transaction passed with a majority vote and 3 of the 5 shareholders voting 'yes' with 92% of the shareholder's vote.
"Out of courtesy, I personally texted Taylor at 9.06pm, Saturday, June 29th to inform her prior to the story breaking on the morning of Sunday, June 30th so she could hear it directly from me.
"I guess it's possible that she might not have seen my text. But, I truly doubt that she 'woke up to the news when everyone else did'."
A spokesperson for Swift said: "Scott Swift is not on the board of directors and has never been.
"On June 25, there was a shareholder phone call that Scott Swift did not participate in due to a very strict NDA that bound all shareholders and prohibited any discussion at all without risk of severe penalty.
"Her dad did not join that call because he did not want to be required to withhold any information from his own daughter.
"Taylor found out from the news articles when she woke up before seeing any text from Scott Borchetta and he did not call her in advance."