Twins John and Edward Grimes, 29, rose to fame after competing in Cowell's music talent show The X Factor in 2009.
Jedward tweeted: "Simon Cowell thinks he’s the Mafia leader of the music industry when in reality he’s nothing but a bad facelift."
Watch: Jedward join Black Lives Matter protest in Hollywood
They continued: "Every contestant on the Xfactor was a slave to the show and got paid Zero while they made millions! The fact that every contestant has to act like their judge mentors them! When in reality all they care about is their pay check!
"There’s a reason Syco is called Psycho! 1D and Little Mix are legally f***ed in contracts and can never speak out so we are! [sic]"
The Lipstick singers claimed to have seen boyband One Direction's contract as the result of an administrative error.
The tweeted: "We have 1D’s contract which was sent to use by mistake cuz we had the same label! Same management! Same security and accountants! Legally posting contracts online is gonna end up in court but we’ve known for many years the situation! Niall! Liam! Louis! Zayn! Harry! You’re survivors."
Jedward claimed to be speaking out in protest against the music industry in a bid to protect musicians' rights.
They tweeted: "It shouldn’t be normal that all artists have to face the emotional and legal battles when all they wanted to do is sing!
"Facts are facts we’re putting ourselves in a very dangerous position speaking out! Victims in the music industry need to be heard! Fans have known for years!
"Artists are on the brink of collapse at the end of touring and having to act like everything is ok! Humans can’t be owned Artists shouldn’t be owned!
"Eating disorders and depression are very common in the music industry and it’s cuz nobody cares about the artist’s mental health! only the money!
"Security hired to watch and report back to management like baby sitters taking away artists Freedom to grow!
"They always isolate artists from their families and make them dependent on fake industry friends who don’t have their back!"
The twins;' comments were echoed by former X Factor finalist Rebecca Ferguson, who is calling for a government inquiry into artist rights and their treatment by the music industry.
Ferguson, 34, claimed she was once worked so hard that she collapsed and no ambulance was called for her.
She tweeted: "At one point in my career I collapsed 3 times in a day I was unconscious! My head hit the floor! No ambulance was called! This is one of many stories. This is the reality of artist mistreatment this is why I fight!"
The Nothing's Real But Love singer revealed on Twitter that she is set to meet culture secretary Oliver Dowden to discuss the issue.
She tweeted: "I am so happy and grateful that the UK will be the country to set a global precedent by creating a 'Music Industry Ombudsman'. Which will change the Music Industry forever and allow Artists to feel safe and protected."
She added: "No more sexually assaulting women in hotel rooms! No more covering up sexual assault for your seedy friends no more grooming 17 year old boys who are confused about their sexuality! No more taking people out of circulation as if they are cattle..."
Ferguson said she had been warned by many people not to speak out as it would be damaging to her career, but added "enough is enough. A lot of my damage has been done, but this is about protecting people in the future."
Watch: Simon Cowell would rather have a broken back than COVID-19