Supreme Court justices raised questions Monday about Washington state's "top two" primary system and whether it discriminates against major political parties.

The system was created after state voters approved a law three years ago to allow voters to pick their favorite candidate for each office, with the top two vote-getters advancing to the November general election, even if they are from the same party.

The major political parties challenged the law in federal court, asserting a First Amendment right to select their own nominees without outside forces interfering.

Several justices appeared wary of the state law, which has been struck down by a federal judge and a federal appeals court.

The law would allow candidates to associate themselves with a party but would not allow the parties to reject a candidate they oppose or simply do not like, said Justice Antonin Scalia.

"That seems to me a great disadvantage to the parties," Scalia said.

Defending the law, state Attorney General Robert McKenna said there was no evidence that the parties would be harmed, since they can publicize through advertising and other means which candidates they support.

Scalia pressed McKenna, asking three times whether the proposed state ballot would indicate that a party does not prefer someone identifying himself as a party member. When McKenna began a lengthy response, Scalia interrupted. "Please answer yes or no," he said.

McKenna finally said no; the ballot would not indicate whether a party endorses candidates identifying themselves as party members.

Chief Justice John Roberts compared the case to a trademark dispute. The two major parties are trying to protect their "brand" to ensure that only those who agree with the party's principles are identified with that party, he said.

Under the law as approved, "people will be confused," Roberts said. Candidates might "look like Republicans but aren't."

Justice David Souter said candidates were unlikely to identify themselves with a party unless they agree broadly with its principles. "That doesn't happen," Souter said.

McKenna disagreed. "There's the example of Sen. Lieberman," McKenna said, referring to the former Connecticut Democrat who lost a party primary after siding with Republicans on waging war against Iraq. Lieberman later won the general election as an independent. He generally caucuses with Democrats in the Senate.

"There's always one," Souter said, drawing laughter from the audience.

The Washington state government and the Washington State Grange have been sparring with the political parties ever since the Supreme Court threw out the "blanket primary" in a California case in 2000.

The blanket primary — adopted as an initiative drafted during the 1930s by the Grange, organized labor and other groups — allowed voters to split their tickets, voting for one party for governor and another party for state senator, for instance.

In 2004, Washington voters approved the Grange-sponsored Initiative 872, which set up the primary system at issue in the case. The major parties challenged the law, which was struck down by a U.S. District judge and the 9th U.S. Circuit Court of Appeals.

John White, arguing the case for Republicans, said the current law converts a party's right to nominate a candidate "to a mere right to endorse," which he said discriminates against the parties.

In recent history, David Duke has identified himself as a Republican, despite GOP repudiation of his racial views. Perennial presidential candidate Lyndon LaRouche has called himself a Democrat, despite wide disagreement with Democratic leaders.