A U.S. citizen has been prevented from leaving China for failing to disclose on his visa application that he worked for the U.S. government, The Washington Post reported.

The Chinese American man, who works for the U.S. Commerce Department’s Patent and Trademark Office, had been visiting family in China but was given an exit ban. U.S. authorities have not identified the man.

Guo Jiakun, a Chinese Foreign Ministry spokesperson, told a regular press briefing on Monday that he had no information to share on the matter, adding: “China is a country upholding the rule of law and we handle relevant cases in strict accordance with the law.”

This is the latest case of a U.S. citizen blocked from leaving China for alleged legal reasons, which in the past have included involvement in business disputes. The practice has alarmed investors and drawn criticism from the U.S. and other governments.

The exact number of foreigners under exit bans in China is not known as some people remain unaware of a ban until they try to leave, with other cases going unreported. The U.S. State Department urges U.S. citizens to “exercise increased caution” when traveling to China due to “arbitrary enforcement of local laws, including in relation to exit bans.”

The U.S. federal employee, who had served in the U.S. Army, has been prevented from leaving China “for months,” Hong Kong’s South China Morning Post reported.

He was initially held in the southwestern city Chengdu, capital of Sichuan province, in April and later traveled to Beijing, accompanied by a U.S. official, although his current whereabouts were not known, the newspaper said.