Customs and Border Protection said Thursday it returned more than 6,000 migrants who arrived at the border without papers since COVID-19-related restrictions were put in place March 21.

The agency has returned 6,375 migrants at the southern border and 20 at the northern border under the policy adopted March 21, according to CBP data. 

The CBP said in a statement that 80 percent of the people its officers encountered at the borders since March 21 were sent back within two hours. 

By turning them back, the administration bypassed the regular processes that would have allowed the migrants to apply for asylum and other protections. Migrants who arrive at the border and claim asylum are typically allowed to make their case to an immigration judge, a process that could take months or even years. 

The Trump administration said in March that it would close the northern and southern borders to non-essential travel in an attempt to contain COVID-19 infections and “reduce the incentive for a mass global migration.” The order to promptly return any migrants lacking papers was issued by the Centers for Disease Control and Prevention. 

At the time, President Donald Trump said at a press conference that the health emergency allowed him to restrict immigration in a way he hadn’t been able to before. He said a “viral spread at our borders” could infect government authorities and “deplete” health care resources in the United States. 

The announcement drew criticism from immigration advocacy groups that said the restrictions were part of Trump’s immigration agenda to stop people from seeking asylum at the southern border. 

Trump invoked a World War II law that permits the president to prohibit “the introduction of persons and property from such countries or places” if deemed likely to introduce communicable illnesses into the country. 

Leaked guidance, reported by investigative news outlet ProPublica, revealed that order directed border agents to send back migrants with little heed to U.S. laws that forbid sending back migrants to countries where they might be persecuted. It is legal to seek asylum in the United States regardless whether a person’s entry was authorized.

At the time of the announcement, Mexico and Central American countries, which are the main sources of migrants to the southern border, had reported far lower cases of COVID-19 than the U.S.

The U.S. currently has more than 430,000 cases and almost 15,000 deaths from COVID-19, according to the Johns Hopkins Coronavirus Resource Center.