By Laura Zuckerman
SALMON, Idaho (Reuters) - A federal judge on Wednesday ruled unconstitutional Idaho's requirement that the Republican party hold an open primary, a decision which, if upheld, could mean an overhaul of the state's election laws.
The ruling stems from a 2008 lawsuit against Idaho brought by the Idaho Republican Party after the state required the GOP to allow Democrats and Independents to vote in its primaries.
In his ruling, U.S. District Judge B. Lynn Winmill agreed with the Idaho Republican Party's claim that its First Amendment right to freedom of association was violated by that requirement.
In court filings, the Idaho Republican Party said it didn't want so-called crossover voters influencing the selection of their nominees for general elections.
Attorneys for the state Republican Party submitted a report that described how strategic crossover voting in a primary election could throw a political party's nomination to a weak or undesirable candidate unlikely to prevail in the general election.
The state argued that the Idaho Republican Party failed to demonstrate damage from crossover voting and that closing primaries would interfere with Idaho's valued tradition of allowing voters to register on election day.
Idaho Secretary of State Ben Ysursa, a Republican, told Reuters on Wednesday he was disappointed by the ruling.
Ysursa said Idaho's open primary system increased voter participation in a state where a large number of voters - an estimated 750,000 - are unaffiliated with a political party.
"Our open primary allowed people to select the party of their choice in the privacy of the voting booth," he said.
Ysursa added that if Idaho decides not to appeal the ruling, state lawmakers will have to craft new election laws.
"This decision will allow the Idaho Republican Party to decide how to conduct its primary elections," Idaho Republican Party Chairman Norm Semanko said in a statement.
(Editing by Dan Whitcomb and Peter Bohan)