Zoom acknowledged that it had shut down and restored the account after the attention.
"Just like any global company, we must comply with applicable laws in the jurisdictions where we operate," a Zoom spokesperson said.
"When a meeting is held across different countries, the participants within those countries are required to comply with their respective local laws.
Zoom said on Wednesday that it had temporarily closed a US account of activists who met to mark the anniversary of China's crackdown in Tiananmen Square, raising alarm over free speech on the fast-growing video-meeting service. US-based rights campaigners turned to Zoom, which has become a way of life for many people during the coronavirus lockdown, to connect more than 250 people to remember Beijing's crushing of the pro-democracy uprising on June 4, 1989. The group Humanitarian China said it had brought in numerous participants from inside China, which has tried to erase memories of the bloodshed -- and that its paid Zoom account was shut down without explanation one week later.
The shutdown was first reported by news site Axios.
"We aim to limit the actions we take to those necessary to comply with local law and continuously review and improve our process on these matters."
The activists voiced outrage, charging that the company may have been under direct pressure from China's communist leaders.
"If so, Zoom is complicit in erasing the memories of the Tiananmen Massacre in collaboration with an authoritarian government," Humanitarian China said in a statement.
It called Zoom an "essential" resource in reaching audiences inside China, which rigorously enforces censorship.
Long dilemma for US tech
Zoom reported Tuesday that its earnings had soared in the quarter ending April 30 as both companies and friends, cooped up inside due to COVID-19 lockdowns, embrace the platform to meet virtually.
Beijing has developed a sophisticated "Great Firewall" that aims to keep out news that is damaging to the leadership.
Authorities go to extraordinary lengths each year to ban commemorations of the Tiananmen crackdown, in which the military killed hundreds of unarmed protesters -- by some estimates, more than 1,000 -- who had packed the capital to seek reform.
PEN America, the literary group that defends free speech, denounced Zoom's move.
"We wouldn't tolerate it if a phone company cut off service for someone expressing their views in a conference call; we shouldn't tolerate it in the digital space either," said the group's CEO, Suzanne Nossel.
"Zoom portends to be the platform of choice for companies, school systems and a wide range of organisations that need a virtual way to communicate, especially amid global lockdown. But it can't serve that role and act as the long arm of the Chinese government," she said.
With its alluring market, China has long been problematic for US tech giants that generally boast of allowing unfettered free speech at home.
Apple in 2017 acknowledged that it bowed to Chinese law by removing apps for VPNs, or virtual private networks, that let its users evade local controls.
A decade earlier, Yahoo faced intense criticism and conceded wrongdoing after helping Chinese officials identify pro-democracy advocates who posted on online message boards.
Its rapid growth has not been without previous problems, with the company forced to confront a rash of racists and other unwelcome gatecrashers who hack into Zoom sessions.
Zhou Fengsuo, a co-founder of the group who was number one on Beijing's most-wanted list after the Tiananmen crackdown, told AFP that the Zoom account was reactivated on Wednesday.
