(NewsNation) — Almost 30 people, most if not all Chinese-Americans, are currently subject to China’s exit ban, The Wall Street Journal reported Sunday.

An exit ban is essentially a government forbidding either its citizens or foreigners from leaving the country. The laws are applied vaguely.

While the U.S has warned China against using exit bans coercively, there is no reliable mechanism or legal process to find out how long an imposed exit ban will last.

The longest-running case involves a Chinese-American businessman named Henry Cai.

The 61-year-old, who has a degree in aerospace engineering, left China in 1988 and moved to California, where he later invested in a former student’s company in China. Then, while visiting the country to manage issues related to his investment, he was told he could not leave.

That was in 2017 and he is still there.

Cai told the WSJ that, despite not being charged with a crime, he fears deteriorating U.S.- China relations will worsen his case, as rapport between the global superpowers has sunk to its lowest in decades.

“So what we’re seeing in terms of the use of the domestic legal system in order to achieve foreign policy goals, this is often labeled as lawfare. So this is a strategy that has been most commonly associated with China, and Russia,” Dr. Dani Belo, an assistant professor of international relations at Webster University, told NewsNation’s “Rush Hour” on Monday.

President Joe Biden met with Chinese leader Xi Jinping on Monday — the first in-person meeting between the two since Biden took office.

Over the course of the three hour meeting, they discussed Taiwan and North Korea, and pledged more frequent communication.

The Dui Hua human rights group is involved in direct conservations with the Chinese government on the issue of detainees. They say an additional 200 or so Chinese-Americans are detained in China on arbitrary grounds.