Missouri’s “Second Amendment sanctuary” law will face its most significant legal challenge yet.

The Department of Justice (DOJ) filed a new lawsuit on Wednesday to prevent the state from enforcing its controversial law that declares certain federal firearms laws invalid. The complaint alleges that House Bill 85, otherwise known as the Second Amendment Preservation Act, discriminates against federal employees and is unlawful under federal law and the U.S. Constitution.

“In light of H.B. 85’s infirmities and the harms to federal law enforcement interests, the United States seeks a declaratory judgment that H.B. 85 is invalid under the Supremacy Clause, is preempted by federal law, and violates intergovernmental immunity,” the complaint reads.

The law has been a lightning rod for controversy since it was enacted last June. It has faced spirited opposition from Missouri Democrats and several police agencies across the state. It also drew immediate fire from the DOJ, who helped support a lawsuit attempting—but ultimately failing—to block the law before it went into effect in August of 2021. Now, DOJ appears to be trying its luck in federal court.

H.B. 85 declared that federal supremacy did not apply to laws that would restrict the right to bear arms. The bill’s text says, “all federal acts, laws, executive orders, administrative orders, court orders, rules, and regulations, whether past, present, or future, that infringe on the people’s right to keep and bear arms as guaranteed by the Second Amendment…must be invalid in this state.” Missouri passed it during the recent “Second Amendment sanctuary” movement, which has seen localities and states across the country adopting various laws prohibiting the enforcement of certain gun restrictions within their jurisdictions.

Missouri is currently one of 17 states with such a law, though its statute contains some unique enforcement provisions not found in other states. The law declares that any state or local official who tries to enforce or assist in the enforcement of any law declared invalid could be subject to a $50,000 civil penalty.

Critics of the law argue this enforcement provision interferes with the ability of law enforcement to do its job and has resulted in police officers pulling back out of fear of a lawsuit. U.S. Attorney General Merrick Garland said it is already impeding “law enforcement operations” in the state.

“The United States will work to ensure that our state and local law enforcement partners are not penalized for doing their jobs to keep our communities safe,” he said in a statement.

Principal Deputy Assistant Attorney General Brian M. Boynton, head of the Justice Department’s Civil Division, said the state of Missouri does not have the authority to ignore federal firearms laws.

“A state cannot simply declare federal laws invalid,” he said. “This act makes enforcement of federal firearms laws difficult and strains the important law enforcement partnerships that help keep violent criminals off the street.”

The new DOJ complaint names Missouri Governor Mike Parsons (R.) and Attorney General Eric Schmitt (R.) as defendants. Schmitt called the new suit an attack on gun rights and said it was politically motivated.

“After their disastrous arguments in the Missouri Supreme Court last week, the Biden Department of Justice has now filed yet another partisan lawsuit that seeks to attack Missourians’ Second Amendment rights,” Schmitt said in a statement. “Time and again, the Biden Administration has put partisan politics ahead of public safety. Make no mistake, the law is on our side in this case, and I intend to beat the Biden Administration in court once again.”

Governor Parsons did not respond to a request for comment.