was last night embroiled in a racism row after a judge on his television show claimed she was told that her hairstyle and clothes were 'too black'.
Actress Gabrielle Union, 47, who was axed last month, is threatening legal action against British entertainment mogul Cowell's company Syco, which co-produces the show.
She claims the working environment on AGT, which attracts about ten million viewers, was 'toxic', that Cowell, 60, a fellow judge, was too dominant and that chatshow host Jay Leno cracked inappropriate jokes when he was a guest.
She also claims there was no mechanism for raising her grievances, even though she talked with Cowell during a meeting at his home in Malibu in May.
A source close to Ms Union told The Mail on Sunday last night: 'She's in discussions with Simon's people and [broadcaster] NBC, but she isn't prepared to back down. This isn't going away. Gabrielle kept complaining about Simon's total autonomy on set.
'There were no other channels to go through to make a complaint about conditions. She was shocked when she was told that her hair and wardrobe was 'too black' and she immediately tried to lodge a complaint, but there wasn't a place to go.'
The source added: 'Gabrielle is powerful and wealthy in her own right. She's not interested in a settlement or having this swept under the rug. This is her #MeToo moment and she's doing this because she genuinely wants to change an outdated system and wants to make it better for the women who come after her.'
It is understood that comments relating to Garbrielle's hair are said to have been made by producers on the show, not Simon himself.
NBC held a five-hour crisis meeting with Ms Union on Tuesday and promised an investigation to 'get deeper understanding of the facts'.
According to US website Deadline, an independent investigator will assess the claims made by Ms Union, who replaced Spice Girl Mel B as a judge this season, joining Cowell, comedian Howie Mandel and dancer Julianne Hough.
In a tweet, the actress – who is married to ex-basketball star Dwyane Wade – wrote: 'We had a lengthy and what I thought to be, productive meeting yesterday. I was able to, again, express my unfiltered truth.'
Her lawyer, Bryan Freedman, said: 'We're waiting to see whether NBC is going to make sure there are real changes made to protect both the contestants and the talent [judges].'
Stars including singer Ariana Grande and actress Patricia Arquette have backed Ms Union.
The Screen Actors Guild and American Federation Of Television And Radio Artists are investigating the departure from the show of Ms Union, a campaigner on women's issues.
In a statement last night, Syco, AGT co-producer Fremantle and NBC said: 'AGT has a long history of inclusivity and diversity… We are working with Ms Union… to hear more about her concerns, following which we will take whatever next steps may be appropriate.'