In a tweet Wednesday, the former judge wrote: “So many tears, so much gratitude. THANK YOU!"
“Just when you feel lost, adrift, alone… you got me up off the ground. Humbled and thankful, forever," the 47-year-old added.
Union's tweet comes after Variety reported Tuesday that her exit was because she spoke out against the alleged “toxic” workplace culture at the NBC singing show.
The report alleges that Union was subject to various racial criticisms, including references to her many hairstyle changes, which were perceived as “too black” for “AGT's” core demographic — a critique Union reportedly received over half a dozen times.
She was also not keen on what some say was a racially insensitive joke by comedian Jay Leno while he was a guest judge.
During the filming of an interstitial segment, Leno joked about a painting that featured Simon Cowell surrounded by dogs. Leno joked that the dogs looked like something one could find “on the menu at a Korean restaurant” — much to the chagrin of “the very few Asian staffers” on the show.
The comment was later edited out of the Aug. 6 episode.
Union allegedly urged producers to report the incident to NBC’s human resources department — but her pleas fell on deaf ears.
The report also noted an episode in which Union took offense to a white contestant impersonating popular acts and people of color through quick costume changes. The contestant impersonated Beyonce and emerged with black hands.
After the actress pleaded with producers to remove the audition, producers reportedly told her, “We’ll take it out later.”
In a joint statement obtained by Variety, NBC and Fremantle -- the production company behind “AGT" -- responded to the allegations, saying: “‘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 lineup has been regularly refreshed over the years and that is one of the reasons for ‘AGT’’s enduring popularity. NBC and the producers take any issues on set seriously.”
Union’s husband, NBC star Dwyane Wade, defended her "firing" on Wednesday.
He wrote on social media: “So when i got the news that my wife was being fired—my first question was obviously why!? Iam still waiting on a good answer to that question. But if anyone knows @itsgabrielleu or have heard of her you know she’s an advocate for our community and culture."
Fox News' Julius Young and Andy Sahadeo contributed to this report.