Tucson’s unusual election system may not be unique after all.

The state of Washington is joining the city’s appeal of a recent opinion from a three-judge panel on the U.S. Ninth Circuit Court of Appeals.

The 2-1 split opinion said Tucson’s election system, which uses a ward-specific primary election and a citywide general election, is unconstitutional because it excludes some voters from the primary election based on the ward in which they live. That’s a violation of the 14th Amendment, the “one-person, one-vote” protection, the majority opinion said.

Judge Alex Kozinski described Tucson’s election system as “unusual” and “odd.”

The city is appealing the decision and asking for a review by an 11-judge panel.

Now, the state of Washington and its Secretary of State have joined the appeal through an amicus brief because 32 of 39 counties in Washington use a similar hybrid election system to elect their county commissioners. Twenty cities and many school districts and special-purpose districts also use hybrid systems to elect city council members and board members, according to the court filing.

“We have used a similar hybrid system for nearly 100 years up here, and it has worked really well for us,” said David Ammons, communications director for Washington Secretary of State Kim Wyman. “It fits our political culture.”

The amicus brief shows the opinion affects a lot more elections than just Tucson’s, Rankin said. Other jurisdictions with similar election systems could join, too, said Tucson City Attorney Mike Rankin.

“We were glad to have them join up and raise some of the same issues we think are important,” he said.

An appeals court decision sets precedent for the entire Ninth Circuit, which includes Arizona, Washington and nine other states and territories.

“The panel opinion threatens far more elections than the majority understood, and it deserves more careful analysis,” Washington’s Deputy Solicitor General Rebecca Glasgow said in the amicus brief.

“It definitely endangers our system if Tucson loses,” Ammons said. “It would totally disrupt our elections process that has been time-honored and something voters are used to.”

Tucson voters chose the hybrid system in 1929, and it has survived many legal challenges. Voters have turned down proposed changes at least three times.

While the court decides whether to accept Tucson’s appeal and whether to keep the ruling or reverse it, voters will likely choose a new election system in 2016, and a citizens committee will help shape the ballot questions.

Additionally, a group is circulating petitions for a ballot initiative that would change Tucson’s system to ward-only elections. The group, Tucsonans for Fair Elections, is led by Timothy DesJarlais, Aaron Taylor and Kile Waldrup.

The group decided to try for a ballot initiative because of the Ninth Circuit decision, DesJarlais said. “Our community should at least have another discussion about this.”

Contact reporter Becky Pallack at bpallack@tucson.com or 573-4346. On Twitter: @BeckyPallack