The Supreme Court declined to revive a controversial Missouri law on Friday that prohibits local law enforcement from helping federal officials enforce federal gun regulations.
The Justice Department had challenged the 2021 law -- called the Second Amendment Preservation Act -- arguing it interferes with the Constitution's Supremacy Clause, which states that federal laws take precedence over state laws.
The state law imposes penalties -- up to $50,000 -- for assisting with the enforcement of federal laws that Missouri's General Assembly believes may be unconstitutional, including those requiring the registration of certain dangerous weapons and others that require firearms dealers to keep records.
The statute does, however, allow state agencies to assist with enforcement of federal laws that have state analogues, such as those involving felony crimes.
A federal judge in the state blocked the law in March, siding with the Biden administration. An appeals court declined to put that ruling on hold, prompting Missouri Attorney General Andrew Bailey to turn to the Supreme Court.
Friday, the court rejected the state's petition.
Justice Clarence Thomas said he would have allowed the law to go into effect. Justice Neil Gorsuch, joined by Justice Samuel Alito, wrote a short statement saying he agreed with the court's order "under the present circumstances."
In his emergency application to the high court, Bailey said that the federal government does not have the legal right known as "standing" necessary to challenge the state law.
"State governments cutting off state resources for federal enforcement is not an injury; it is a feature of a State's settled Tenth Amendment authority," Bailey told the justices.
The 24-page decision issued in March by US District Judge Brian Wimes ruled that the law is "invalidated as unconstitutional in its entirety."
"State and local law enforcement officials in Missouri may lawfully participate in joint federal task forces, assist in the investigation and enforcement of federal firearm crimes, and fully share information with the Federal Government without fear of (SAPA's) penalties," Wimes wrote.
The law's "practical effects are counterintuitive to its stated purpose," added Wimes, a nominee of former President Barack Obama.
"While purporting to protect citizens, SAPA exposes citizens to greater harm by interfering with the Federal Government's ability to enforce lawfully enacted firearms regulations designed by Congress for the purpose of protecting citizens within the limits of the Constitution," he wrote.
Solicitor General Elizabeth Prelogar called the Missouri law "patently unconstitutional" in court papers opposing the emergency request.
"As this court has long recognized," she wrote, "the Supremacy Clause precludes a State from nullifying federal law or interposing obstacles to the enforcement of federal law."
US law enforcement officials previously told CNN that federal agents have encountered a number of issues in the state since the law went into effect because local authorities were worried about potentially violating it.