China's government has been accused of silencing the 36-year-old player after she made a sexual assault allegation in November.
Tennis Australia has been criticised by former and current stars for banning t-shirts supporting absent Chinese player Peng Shuai.
Spectators attending the tournament in Melbourne have been blocked from publically displaying their support for Peng.
Viral videos have shown security officials and police requesting one supporter to remove a t-shirt that featured an image of the Chinese player and the words “Where is Peng Shuai?”
Concerns have been raised about the 36-year-old's welfare after she made a sexual assault allegation last year against a close ally of President Xi Jinping.
Peng has since reappeared, but the Women's Tennis Association (WTA) has refused to play any tournaments in China this year.
Tennis Australia is the latest to face backlash for its stance on the matter, with Martina Navratilova and Nicholas Mahut among the critics.
Navratilova -- a former Women's Number 1 and three-time Australian Open champion -- said the ban on t-shirts and banners was "pathetic".
"I think it's really cowardly," she added in an interview on the Tennis Channel. "This is not a political statement, this is a human rights statement."
Seeded men's doubles player Mahut meanwhile drew attention to Chinese alcohol brand Luzhou Laojiao, one of the sponsors of the tournament venue, Melbourne Park.
"What’s going on!? What lack of courage!," Mahut said on Twitter. "What if you did not have Chinese sponsors? Beyond disappointed."
A GoFundMe page seeking support to distribute Peng Shuai shirts at the Australian Open had raised thousands of dollars within 24 hours over the weekend.
Tennis Australia initially stated that t-shirts featuring the words "Where is Peng Shuai" broke their rules on "political" statements.
The authority later responded to the backlash, saying it understood “people have strongly held personal and political views on a range of issues”.
“Peng Shuai’s safety is our primary concern. We continue to work with the WTA and the global tennis community to do everything we can to ensure her well-being," the statement said. "Our work is ongoing and through the appropriate channels.
“To ensure that the Australian Open remains a welcoming, safe and inclusive event for everyone, we have a longstanding policy of not allowing banners, signs, or clothing that are commercial or political."
Chinese Foreign Ministry spokesperson Zhao Lijian said China was “always opposed to the politicisation of sports".
"Such actions are unpopular and will never succeed,” Zhao said when asked about the Peng Shuai t-shirts.
But human rights activists have called on other athletes at the Australian Open to bring attention to concerns for the Chinese player's safety.
On 20 December, Peng denied making the allegations of sexual abuse and claimed to have been at home without any surveillance during the time she was missing.
The former top-ranked doubles player had a video call with Olympic officials in late November after the European Union called on China to release "verifiable proof" that Peng is safe.