Hawaii Democrats are appealing a federal judge’s ruling that upholds the state’s primary election system, which allows voters to choose which party’s primary they want to vote in no matter how they’re registered.

Party officials filed a notice of appeal in federal court in Hawaii on Thursday. The notice says the party is appealing to the 9th U.S. Circuit Court of Appeals.

The party argues that allowing every registered voter to participate in its nominations is equivalent to forced political association.

A federal judge in Hawaii ruled last month that the party failed to prove the system is unconstitutional.

Hawaii has allowed voters to choose which primary they want to vote in since 1980.

Gov. Neil Abercrombie, a Democrat, has said he agrees with the open system.