Uber’s head of HR has resigned after only a 18 months tenure, following an investigation into how she handled allegations of racial discrimination at the taxi firm.

Liane Hornsey, the firm’s chief people officer, was accused by anonymous whistle-blowers of systematically dismissing internal complaints of racial discrimination.

She resigned in an email to staff on Tuesday. 

The exit came after an anonymous employee emailed Uber’s whistle-blower account and chief legal officer Tony West threatened to go public with grievances if the company didn’t take action.

The whistle-blower accused Hornsey of dismissing internal allegations of racial discrimination, according to a person who read the email. Bloomberg hasn’t obtained a copy of the complaints.

The allegations raise questions about chief executive Dara Khosrowshahi’s efforts to change the toxic culture of the firm after he took over in August last year from Uber founder Travis Kalanick following a series of scandals.

Khosrowshahi praised Hornsey as “incredibly talented, creative, and hard-working” in an email to employees but gave no reason for her departure.

Hornsey did not respond to requests for comment about the investigation.

Unnamed staff members  claiming to be ‘Uber employees of colour’ also claim Hornsey used discriminatory language about two fellow Uber executives, including Uber’s Global Head of Diversity and Inclusion, Bernard Coleman and Uber executive Bozomo Saint John.

After the complaint against her law firm Gibson Dunn launched an investigation into the allegations.

Uber told Reuters in a statement that the complaints had been properly investigated.

“We are confident that the investigation was conducted in an unbiased, thorough and credible manner, and that the conclusions of the investigation were addressed appropriately,” it said.