China’s most popular social media service has deleted accounts on LGBT topics run by university students and nongovernment groups, prompting concern the ruling Communist Party is tightening control over gay and lesbian content.

WeChat sent account holders a notice they violated rules but gave no details, according to the founder of an LGBT group, who asked not to be identified further out of fear of possible official retaliation. She said at least dozens of accounts were shut down, all at about 10 p.m. on Tuesday.

It wasn’t clear whether the step was ordered by Chinese authorities, but it comes as the ruling party tightens political controls and tries to silence groups that might criticize its rule.

WeChat’s operator, Tencent Holding Ltd., confirmed it received an email seeking comment but didn’t immediately respond.

The Communist Party decriminalized homosexuality in 1997, but gay, lesbian, bisexual, transsexual and other sexual minorities still face discrimination. There is more public discussion of such issues, but authorities have blocked some LGBT activities.

The official attitude is increasingly strict, the founder of the LGBT group said.

Contents of the WeChat accounts, which included personal stories and photos of group events, were erased, according to the group founder.

The former operator of a different group for university students, who asked not to be identified for fear of retaliation, called the step a devastating blow.

University officials asked students two months ago to shut down LGBT social media groups or to avoid mentioning their school names, according to the LGBT group founder. She said universities in the eastern province of Jiangsu were told by officials to investigate groups for women’s rights and sexual minorities to “maintain stability.”