A federal appeals court is upholding an earlier decision to support the way Hawaii holds its primary elections, rejecting the Democratic Party’s desire to exclude non-Democrats from advancing candidates to the general election.

The Democratic Party of Hawaii had challenged the state’s open primary system, in which registered voters can choose any party’s ballot to cast their votes without formally joining the party. Party leaders wanted to limit primary elections to formal members or people willing to declare their allegiance, because they said the open primary system allows people from opposing parties to influence their party’s candidate selection.

Judge Wallace Tashima of the 9th Circuit Court of Appeals said it was up to the Hawaii Democratic Party to prove that a problem exists. But he said in an opinion Monday the party didn’t provide evidence that opponents are determining the Democratic Party’s election outcomes.

“Absent evidence that Hawaii’s system affects the party’s ability to select its nominees, the party’s facial challenge failed,” Tashima wrote.

Tim Vandeveer, chairman of the Democratic Party of Hawaii, said the party had not yet decided whether it would appeal the decision.

“Our executive committee has to discuss that very seriously,” Vandeveer said, adding that regardless of his own opinion, it won’t be his decision alone.

“I was elected (party chairman) as a Bernie San-ders supporter, and Sanders has been a very big proponent of open primaries,” Vandeveer said. “The progressive wing of our party is very pro-open primary.”

Hawaii is one of 15 states with open primaries, meaning voters can select any one party’s ballot to cast their votes on Election Day.

“The open primary is part of Hawaii’s commitment to make voting easier and to include more persons in the democratic process,” said state Attorney General Doug Chin in a statement. “This ruling keeps Hawaii’s primary elections open to all registered voters, regardless of their formal party affiliation.”

Only nine states have closed primaries in which voters have to register with a party in advance to cast a primary vote, the National Conference on State Legislatures says. Those closed primaries are designed to keep voters from “crossing over” and casting ballots in their opponent’s primary election.