A bipartisan group of U.S. lawmakers have grown concerned over China detaining American citizens while visiting the country, and have proposed legislation Wednesday that would put sanctions on Chinese officials involved with the “exit bans.”

“It is immoral and unjust that the Communist Chinese government uses so-called ‘exit bans’ to prevent American citizens from leaving China. We must protect our citizens and ensure that they are able to return home when they travel abroad,” Sen. Marco Rubio, R-Fla., said in a statement.

Sen. Ed Markey, D-Mass., also backed the legislation.

Siblings Cynthia Liu, 28, and Victor Liu, 20, two American citizens from Massachusetts, are currently stuck in China due to the exit ban and were detained in China in June 2018.

The Lius were visiting China to see their ailing grandfather and went on the trip with their mother, Sandra Han, who is also a naturalized U.S. citizen. Han was detained shortly after arrival in China.

The Chinese government is essentially taking the entire family hostage in order to pressure their father Liu Changming, a former bank executive and fugitive, to return after he fled in 2007.

“They are trapped. They are alone. They are desperate to come home,” David Pressman, the siblings’ attorney told USA Today in September. Cynthia and Victor Liu are allowed to travel freely within China but are forbidden from returning home.

Huang Wan, an American citizen, has also been held in China since 2016 due to the exit ban. Her father-in-law is a former top Chinese official who is serving a life sentence for corruption.

The legislation would deny or revoke visas of any Chinese officials involved with the exit ban policy. The legislation is being introduced as the U.S. and China sign the “Phase 1” trade deal, which will de-escalate trade tensions between the two nations.