WASHINGTON (AP) — A coalition of conservative-leaning states is making a last-ditch effort to uphold a Trump-era health rule that allows many asylum seekers to be turned away at the U.S. southern border.

Late Monday, the 15 states filed what is known as an intervention motion — meaning they want to be part of the court process surrounding the public health rule known as Title 42.

The rule, first invoked by Trump in 2020, uses the public health emergency agency to allow the United States to block migrants from seeking asylum at the border because they must help stop the spread of to prevent COVID-19.

It is scheduled to end on December 21 and potentially upend border enforcement as Republicans are about to take control of the House from Democrats after the midterm elections and plan to make immigration a central part of their agenda .

States argued that they would suffer “irreparable harm from the impending termination of Title 42” and that they should be allowed to assert their position well before the December 21 termination date.

In a statement, an attorney for the American Civil Liberties Union, which has campaigned to end the use of Title 42, questioned states’ motivation for trying to keep the public health rule in place.

“Title 42 is not about general asylum border enforcement, it’s about public health, and these states cannot plausibly claim that their real interest is public health,” Lee Gelernt said.

Immigration rights groups have argued that the use of Title 42 unfairly harms people fleeing persecution and that the pandemic was an excuse used by the Trump administration to curb immigration. A judge ruled in favor of the immigrant rights groups on November 15, calling the ban “arbitrary and capricious.”

US District Judge Emmet Sullivan ruled in Washington that enforcement for families and single adults must end immediately. The Administration has not used Title 42 in relation to children traveling alone. The judge later granted a request by President Joe Biden’s administration to set a deadline of December 21 for his order to go into effect, giving the administration five weeks to prepare for the change.

The 15 states argued that states like Arizona and Texas that border Mexico, as well as other states across the border, will face more immigration when use of Title 42 ends. The legal filings contain a timeline to further discuss the matter.

If Sullivan’s ruling stands, it could have a dramatic impact on border enforcement. Migrants have been deported from the United States more than 2.4 million times since the rule went into effect in March 2020.

Sullivan’s ruling appears to be at odds with another ruling in May by a Louisiana federal judge that upheld asylum restrictions. Before the Louisiana judge’s decision, U.S. officials said they expected up to 18,000 migrants a day in the worst-case scenario, a staggering number. By comparison, migrants were stopped an average of 7,800 times a day in May, the highest number in Biden’s presidency.

The ban has been unevenly enforced by nationality, mostly hitting migrants from Guatemala, Honduras and El Salvador — in addition to Mexicans — because Mexico allows them to be deported from the United States. Last month, Mexico began accepting Venezuelans expelled from the United States under Title 42, prompting a sharp drop in the number of Venezuelans seeking asylum at the US border.

The Biden administration initially approached the Centers for Disease Control and Prevention to keep Title 42, despite opinion from some in the president’s own party, as well as activist groups skeptical of the need for the public health rule. In April, the CDC said it would end the public health order and return to normal border processing for migrants, which would give them the ability to seek asylum in the US to use Title 42.

The 15 states that submitted the request for intervention are Arizona, Alabama, Alaska, Kansas, Kentucky, Louisiana, Mississippi, Nebraska, Ohio, Oklahoma, South Carolina, Texas, Virginia, West Virginia and Wyoming.