BEIJING (Reuters) – Zoom Video Communications (ZM.O) has gained a following in China in recent months from users ranging from underground churches to feminists who saw it as a rare way to connect with the world beyond the reach of state censors.

Some fear that window may be closing.

On Friday, Zoom said it had suspended accounts of three U.S. and Hong Kong activists at Beijing’s request after they tried to commemorate the anniversary of the Tiananmen Square crackdown, but that they had since been reactivated. The U.S. company also said it was developing technology to enable it to remove or block participants based on geography.

The Chinese government heavily regulates the internet, in a system widely dubbed the Great Firewall, saying this is needed to maintain social stability. All Chinese social media platforms are required to censor public posts deemed illegal.

“For us, the biggest challenge has been how to reach people within China because of the firewall, and Zoom for a while looked like a ray of hope,” said U.S.-based Humanitarian China founder Zhou Fengsuo, whose account was suspended.

The conferencing tool, originally designed for business use, saw Chinese user numbers surge in tandem with its global popularity amid the COVID-19 pandemic, a rare feat given how Western peers such as WhatsApp, Google Meet and Facebook are blocked in China’s cyberspace.

Zoom’s mobile app has been downloaded 5.4 million times from Apple’s China store since Jan. 1, 11 times the number over the same period in 2019, according to research firm SensorTower.

While most Chinese users turn to Zoom for conference calls and casual chats, some have seized the chance to discuss potentially sensitive topics, from patriotism to feminism.

Some state-approved and underground churches use Zoom to hold services.

“Zoom is not the only software, but we feel it’s rather more accessible,” said Xiao Meili, a feminist activist who held a Zoom talk in April on the #MeToo movement.

“Before, some friends recommended Tencent conference … but everyone would feel like you shouldn’t say anything that’s slightly sensitive,” she said, referring to a tool offered by the Chinese tech giant behind WeChat.

INSIDE THE FIREWALL

In March, Youth Lectures kicked off a series of Zoom talks, the first of which was led by Chinese University of Hong Kong professor Chow Po Chung, on freedom of speech in China. Chow’s mainland China account on the Twitter-like platform Weibo has been deleted multiple times.

Other anonymous groups hosted lectures from a #MeToo activist and a gender-activist on their work in mid-May.

New York-based Lu Pin, whose influential Feminist Voices accounts on Weibo and WeChat were shut by authorities in 2018, said Zoom was a way to connect a Chinese audience to the outside world.

“You don’t have to climb the firewall, people in China and outside of China both can connect to it,” she said.

There are few alternatives, she said.

“This is not a multiple-choice question. If you’re a Chinese person, if you don’t use this, what will you use?”

Zoom’s China users had already been subject to new constraints since last month when the company announced that free users would no longer be able host meetings, and new registrations were limited to some enterprises.