A new report alleges Union's departure from the show came after she made several complaints to NBC execs.
The incident reportedly involved the comedian making an off-the-cuff remark about a portrait of Simon Cowell alongside his dogs. Leno allegedly joked that the dogs looked like they would be "on the menu at a Korean restaurant."
The alleged joke reportedly offended a few staff members, since it was viewed as perpetuating stereotypes about Asian cultures eating dog meat.
Union urged producers of the show to report the incident to NBC's Human Resources department. She reportedly had a conversation with an NBC exec, but the incident was never brought to HR, according to Variety. Leno's comment was cut before the segment aired.
NBC and Fremantle, the production company behind AGT, responded to the reports and allegations on Tuesday, telling ET in a statement, "America’s Got Talent has a long history of inclusivity and diversity in both our talent and the acts championed by the show.
"The judging and host line-up has been regularly refreshed over the years and that is one of the reasons for AGT’s enduring popularity," the statement continued. "NBC and the producers take any issues on set seriously."
Another incident occurred during an audition taping and involved a white male contestant, whose talent was quick-changing between costumes.
At one point, his act reportedly involved him wearing dark make-up on his hands for a bit in which he dressed like Beyonce. Variety reports Union objected to the act being involved in the show, even though producers reportedly disagreed, and brought up that the show’s live audience should not be subjected to anything that is racially insensitive. The contestant was cut before the audition rounds aired.
Additionally, Variety reports that sources, who agreed to speak to the publication on the condition of anonymity, claimed Union received specific critical network notes on her hairstyles, which were allegedly deemed "too black" for the AGT audience, and that she received these notes numerous times. A network insider denied the volume of those notes to Variety, claiming that there were only notes about "hair continuity" for both her and Hough.
This was Hough and Union's first season as judges on the series, after stepping in for former judges Mel B and Heidi Klum. Judges Simon Cowell and Howie Mandel, as well as host Terry Crews, are expected to return next season.
ET has reached out to Union, Hough, Mandel, Cowell and Crews for comment.
Meanwhile, ET caught up with Union after the AGT finale in September, where she told ET that she "didn't know" if she would return to the show.
"There's a lot of amazing things happening, but I love this show. I love the opportunity of being a part of peoples' dreams coming true. I'm on the talent side, where I get rejected every day, and it was nice to really, kind of, go a little deeper with each contestant and really be a part of their dream," she said, adding, "Hopefully they'll have me back."
For more on Union, watch the video below.