The president of the Women’s Tennis Association has demanded that China investigate Chinese tennis player Peng Shuai’s allegations against former Vice Premier Zhang Gaoli, taking a rare public stance against Beijing on a political controversy.

Peng’s statement earlier this month marked the first time a senior Chinese politician has been publicly accused of sexual assault. Her online post was quickly censored in China, and she has remained silent since, raising questions about her whereabouts and safety.

In 2014, Peng, 35, became the first Chinese tennis player to be ranked No. 1 in doubles by the Women’s Tennis Association. Zhang, four decades her senior, served as China’s vice premier from 2013 until his retirement in 2018.

WTA Chairman Steve Simon said in a statement on Sunday that Peng displayed “remarkable courage” in making her statement and called for a full investigation of the allegations without censorship.

“Her allegation about a former Chinese leader’s conduct involving a sexual assault must be taken seriously,” Simon said in a statement. “In all societies, the behavior she claims occurred should be investigated, not condoned or ignored.” A screenshot of a post allegedly from Peng’s verified Weibo microblog account circulated in China earlier this month, prompting censors to scramble to delete copies. According to the post, Zhang had pressured Peng into having sex with him in his home several years prior before convincing her to engage in a long-term affair with him.

“At first, I didn’t agree and kept crying,” the post said.

Such an allegation against a top leader is almost unheard of in China, where senior officials keep their personal lives shrouded in secrecy. The Chinese Communist Party forbids officials from having extramarital relationships, and it has been used as a reason for dismissal at lower levels of government.

The WTA statement comes at a time when international sports organizations are finding it increasingly difficult to enter China’s massive consumer market without getting involved in politics. For years, conventional wisdom held that businesses seeking to court Chinese consumers should avoid political issues and any criticism of Beijing.

However, as diplomatic tensions between China and the West have escalated, sports leagues have found themselves caught between a business backlash in China if they do not toe Beijing’s political line and consumer boycotts in the West if they do not stand up to China on human rights issues.

China cut the Boston Celtics’ live broadcasts last month after center Enes Kanter posted a video supporting Tibetan independence, which Beijing regards as an illegal secessionist movement. Two years ago, the NBA faced backlash in China after Houston Rockets General Manager Daryl Morey expressed support for Hong Kong pro-democracy protesters. Peng’s silence has alarmed tennis fans around the world. Chris Evert, the 18-time Grand Slam champion, tweeted on Sunday that Peng’s allegations were “very disturbing.”

“I’ve known Peng since she was 14 years old; we should all be worried; this is serious; where is she?” “Is she okay?” Evert made a post.

“I can’t believe this is even happening in the twenty-first century,” wrote British tennis player Liam Broady on Twitter.

Chinese feminists have also attempted to raise awareness of the case by projecting “Where is Peng Shuai?” and other messages of support on the sides of buildings. On Monday, the WTA’s call for an investigation appeared to be censored in China, with few mentions appearing on social media platforms in the country. Simon’s statement was not carried by the WTA’s Chinese-language Weibo account, which has 400,000 followers.