The depositors were planning to travel to the central province of Henan this week from across China to protest against an almost two-month block on accessing at least $178 million of deposits, which has left companies unable to pay workers and individuals unable to access savings.
Rights groups have warned China could use its vast COVID surveillance infrastructure to stifle dissent. Without a green code on their smartphone app, citizens lose access to public transport and spaces such as restaurants and malls, as well as the right to travel across the country.
"They are putting digital handcuffs on us," said a depositor from Sichuan province surnamed Chen, who declined to use his full name for fear of government retribution.
The Henan provincial government, the National Health Commission and the Ministry of Public Security did not respond to requests for comment.
After recent COVID outbreaks, some regions in China have asked travellers to register their plans online.
A man surnamed Liu, who lives in Hubei province, found that his health code turned red on the morning of June 12 after he registered the day before to travel to Henan.
Liu had planned to travel to a protest planned for Monday in the Henan provincial capital Zhengzhou, where he had hoped to get his money back. The protest would have been the latest among numerous such demonstrations in Henan in recent months.
More than 200 depositors were similarly blocked when their health codes turned red, according to members of a WeChat group.
It could not be ascertained if the change in code was intended to block the protesters or for another reason, but three depositors told Reuters they knew people who had registered to travel to Henan, who were not connected to the frozen funds, whose codes did not turn red.
Yu Zhou Xin Min Sheng Village Bank, Shangcai Huimin Country Bank and Zhecheng Huanghuai Community Bank froze deposits on April 18, with all three telling customers they were upgrading internal systems.
Liu, who declined to give his full name for fear of government repercussions, said his child may not be able to go to school if his code does not soon revert to green.
"I can't do anything, I can't go anywhere. You're treated as though you're a criminal. It infringes on my human rights," said Liu.
Wang Qiong, who lives in the central city of Wuhan, found her health code had turned red after she registered to travel to Henan on June 11.
"The police had my identity details from the last time I went to protest in April," said Wang, who said she has lost access to 2.3 million yuan ($341,550).
Other depositors told Reuters they were able to arrive in Zhengzhou by train and car but their codes turned red as soon as they scanned city health codes.
($1 = 6.7340 Chinese yuan renminbi)
(Reporting by Engen Tham; Additional reporting by Martin Quin Pollard; Editing by Tony Munroe and Mark Potter)
By Engen Tham