After Union's contract was not renewed for a second season last month, Variety reported that her departure came after she complained about inappropriate behavior involving talent and producers on the show, as well as racially insensitive events.
NBC responded to the reports in a statement.
"We remain committed to ensuring a respectful workplace for all employees and take very seriously any questions about workplace culture. We are working with Ms. Union through her representatives to hear more about her concerns, following which we will take whatever next steps may be appropriate."
According to Variety, Union was told her hairstyles were "too black" for the audience, and urged producers to contact human resources after guest judge Jay Leno allegedly made a joke "seen by people present as insensitive to Asian communities."
The joke never aired on the show and the situation was not escalated to human resources, Variety reported.
She was also allegedly labeled as "difficult" by Simon Cowell and producers of the show after she complained about him smoking indoors, according to Vulture.
Union, Cowell and Leno did not respond to TODAY's request for comment.
Union's husband, retired NBA star Dwyane Wade, came to her defense after she was fired.
"As proud as i were of her being selected as a judge on #AGT— I am even more proud of her standing up for what she stands for and that’s US,'' he wrote.
Actresses Ellen Pompeo and Debra Messing and pop star Ariana Grande are among those who have come to Union's defense.
Union hasn't responded directly to the reports, but quote-tweeted a message about making solid apologies and thanked her fans for their support.
"So many tears, so much gratitude,'' she wrote. "THANK YOU! Just when you feel lost, adrift, alone... you got me up off the ground. Humbled and thankful, forever."
Union isn't the only judge who won't be returning for the next season of "America's Got Talent," as actress Julianne Hough also did not have her contract renewed.