A Browning .30-caliber belt-fed machine gun was among the weapons Tucson police seized in 2009.

Kelly Presnell / Arizona Daily Star 2009/

The city of Tucson is asking the Arizona Supreme Court to throw out a lawsuit filed by Attorney General Mark Brnovich over the city’s policy to destroy confiscated guns.

The 30-page motion filed Thursday night suggests the legal mechanism that brought the complaint to the state’s highest court — SB 1487 — is unconstitutional and, therefore, unenforceable.

The state’s lawsuit threatens to pull shared revenue from the city unless Tucson stops destroying seized guns. Tucson receives $115 million a year in state-shared revenue.

Additionally, city officials argue the gun-destruction policy — which applies to handguns and semi-automatic firearms — is a protected action, since Tucson is a charter city.

Tucson is among 18 cities that have taken advantage of a constitutional provision allowing them to write their own charters — legal documents that spell out the functions and powers of a city.

The filing also asks the Supreme Court to instead have a lower court to hear the case — the city has filed a case in Pima County Superior Court.

Attorneys for the city, Richard M. Rollman and Richard A. Brown, argue that the Legislature wrote SB 1487 in an effort to force local municipalities into rescinding controversial policies. Signed by Gov. Doug Ducey earlier this year, it restricts local governments from passing any laws that conflict with state laws, jeopardizing their state-shared revenue if they don’t repeal such laws.

“It may be that the Legislature disagrees with the authority given to charter cities by the constitutional framers. But, rights granted by the constitution can only be withdrawn by a constitutional amendment that is approved by the voters pursuant to Article 21 of the Arizona Constitution,” the attorneys wrote.

They also wrote that the new law “seeks to avoid that requirement by coercing any city that seeks to exercise its charter city authority through the prospect of catastrophic financial sanctions without judicial review.”

If the Supreme Court refuses to throw the case out, the city has asked the high court to consider the constitutionality of SB 1492 as part of the overall complaint.

State Rep. Mark Finchem, an Oro Valley Republican, filed the complaint with the Attorney General’s Office earlier this year, stating Tucson is violating an Arizona law that requires the sale of otherwise legal guns obtained by law enforcement agencies. These firearms are typically seized in criminal cases.

The Tucson City Council voted earlier this month to reject Brnovich’s demand that it repeal its 2005 city ordinance requiring the destruction of most handguns and semi-automatic firearms seized by police.

The council also decided at the same time to indefinitely suspend the destruction of firearms until the court fight has been resolved.

Contact reporter Joe Ferguson at jferguson@tucson.com or 573-4197. On Twitter: @JoeFerguson