Timnit Gebru, a co-leader of Google’s Ethical Artificial Intelligence team, said late Wednesday that she’d been abruptly fired from the search giant over an email she sent to colleagues.

Gebru, a prominent AI researcher, has done studies on the dangers of facial recognition bias and has spoken out on the lack of diversity in the tech industry. In the wake of her departure, more than 1,400 Google workers, as well as more than 1,800 other industry professionals, signed an open letter in support of Gebru.

“Instead of being embraced by Google as an exceptionally talented and prolific contributor, Dr. Gebru has faced defensiveness, racism, gaslighting, research censorship, and now a retaliatory firing,” the letter read.

In a series of tweets Wednesday night, Gebru said she was terminated for a message she sent to Google Brain Women and Allies, an internal email list at the company. After sending the email, Gebru said she received a note from her manager telling her the message was “inconsistent with the expectations of a Google manager.”

Gebru didn’t publicly share the contents of her initial email to the Brain group. But the email reportedly criticized Google’s Diversity, Equity and Inclusion operation for being unaccountable, according to Platformer, which posted the message. “So if you would like to change things, I suggest focusing on leadership accountability and thinking through what types of pressures can also be applied from the outside,” Gebru wrote.

In the email, Gebru said she had been working on a research paper with colleagues when she was abruptly asked to retract it without explanation. Gebru said on Twitter that she emailed her manager the research paper, apparently giving the company a list of demands to be met. She said she didn’t resign, but that her manager emailed Gebru’s direct reports to say she “accepted my resignation.” After that, Gebru said her corporate email account had been shut down.

In an email to employees on Thursday, first published by Platformer, Google head of AI Jeff Dean said one of Gebru’s requests was to identify every person that Dean and Gebru’s manager consulted as part of the paper’s review process. He urged employees to continue working with Google’s diversity programs, as well. “I also feel badly that hundreds of you received an email just this week from Timnit telling you to stop work on critical DEI programs,” Dean wrote. “Please don’t.”

Gebru didn’t respond to a request for comment. Google declined to comment beyond Dean’s email.

After Gebru said on Wednesday that she’d been fired, former Google employees began tweeting “I support @timnitGebru.”

The incident with Gebru comes as Google has already drawn intense criticism for its handling of labor issues. On the same day as Gebru’s tweets, Google was accused by the US labor board of retaliating against workers who organized protests against the search giant. In a complaint from the National Labor Relations Board, the federal agency said Google broke US labor laws by surveilling, interrogating and firing activist employees.

Over the last few years, Google has faced tumult as it’s dealt with uprisings from its workforce. Rank-and-file employees have spoken out against the company’s work in China, its contracts with the US military, and Google’s handling of sexual misconduct allegations against senior executives.

Gebru’s exit also drew blowback from critics already worried about Google’s work in ethical AI. When Google assembled an AI ethics board last year, the company came under fire last year for the people chosen to comprise the panel. One member, the Heritage Foundation’s Kay Cole James, was accused of being anti-immigrant and homophobic. The board was disbanded just over a week after it was announced.