(NewsNation) — Whether proper public notice procedures were followed by the Centers for Disease Control and Prevention was at the center of arguments made in front of a federal judge Friday on whether the Biden administration can lift pandemic-related restrictions later this month on immigrants requesting asylum.

Migrants have been expelled more than 1.8 million times since March 2020 under federal Title 42 authority, which has denied migrants a chance to request asylum under U.S. law and international treaty on grounds of preventing the spread of COVID-19.

The administration’s plan to end the Title 42 authority was announced by the CDC April 1. The plan has drawn criticism from Republicans and some Democrats fearing a flood of new migrants

Louisiana, Arizona and Missouri quickly sued and were later joined by 18 other states in the legal challenge being heard Friday. Texas sued independently.

Arizona attorney Drew Ensign, who was making arguments for all 21 states, argued the CDC did not follow proper administrative procedures requiring public notice and gathering of comments on the decision to end the restrictions imposed under what is known as Title 42 authority.

The result, he said, was that proper consideration was not given to likely resulting increases in border crossings and their possible effects, including pressure on state health care systems and the diversion of border law enforcement resources from drug interdiction to controlling illegal crossings.

Jean Lin, with the Justice Department, argued that the CDC was within its authority to lift an emergency health restriction it felt was no longer needed. She said the CDC order was a matter of health policy, not immigration policy.

“There is no basis to use Title 42 as a safety valve,” Lin told U.S. District Judge Robert Summerhays, the judge in the case, in Lafayette, Louisiana.

The lawsuit comes as migrants have attempted to cross the U.S.-Mexico border at the highest level in two decades in March, according to U.S. Customs and Border Protection data. The number of illegal crossings, or those outside official ports of entry, totaled 209,906 in March, surpassing the previous high of Joe Biden’s presidency of 200,658 set in July, and the highest level since March 2000, when it reached 220,063.

After the administration acknowledged last month that it had already begun phasing out the pandemic restriction by processing more migrants under immigration law instead of Title 42, Summerhays ordered the phaseout stopped.

An appointee of President Donald Trump, Summerhays wrote last month that winding down restrictions before May 23 would inflict “unrecoverable costs on healthcare, law enforcement, detention, education, and other services” on the states seeking to keep the policy in effect.

He also said the administration likely failed to follow federal rule-making procedures in planning the May 23 end of the policy. Friday’s arguments are on whether to keep restrictions in place beyond May 23 while litigation proceeds. It was unclear how quickly Summerhays would rule.

Title 42 authority has been applied unevenly across nationalities. Mexico has agreed to take back migrants from Guatemala, Honduras, El Salvador and Mexico — and limited numbers from Cuba and Nicaragua. High costs, strained diplomatic relations and other considerations have made it more difficult to remove migrants from other countries, who must be flown home.

Title 42 is one of two major surviving Trump-era policies to deter asylum at the border. Last month, the Supreme Court heard arguments on whether to allow the U.S. to force asylum-seekers to wait in Mexico for hearings in U.S. immigration court.

The Associated Press contributed to this report.