PHOENIX — Arizona laws that require would-be voters to produce documents proving they are U.S. citizens don't amount to an unconstitutional poll tax, a federal judge ruled.

U.S. District Judge Roslyn Silver rejected various contentions of the Mexican American Legal Defense and Educational Fund that the requirements of a 2004 voter-approved measure are discriminatory or unconstitutional. They require both proof of citizenship to register and presentation of certain forms of identification to cast a ballot.

"Only citizens may vote," Silver wrote. "Requiring an individual to present proof of citizenship allows the state to determine if that individual is qualified to vote."

This week's ruling does not end the legal challenge. MALDEF still is entitled to pursue two other claims at trial, including one that the measure is illegal because it disproportionately depresses Hispanic voting strength.

But Silver, in the new ruling, found nine of the group's contentions so lacking in merit that she agreed with attorneys for the state that they should be thrown out even before a trial.

Nina Perales, regional counsel for MALDEF, said the ruling was not surprising. The judge had previously rejected a request for a restraining order to block the state from using the new requirements in the 2006 election.

Perales said she believes a federal appeals court will conclude otherwise.

But Secretary of State Jan Brewer said the ruling confirms her belief that Arizona has an "inherent right" to ensure that people who are casting their ballots are legally entitled to do so.

Perales is not contesting laws requiring people to be citizens to register. Instead she contends the requirement to produce certain kinds of documents is illegal.

That led to the argument that the ID mandate amounts to an unconstitutional "poll tax," as people would need to purchase certain documents to vote. She said that issue crosses ethnic lines because anyone who is poor and does not have a driver's license, one of the acceptable documents, would be denied the right to vote.

But Silver said the requirement does not rise to the level of a fee to vote, which would be illegal.

The judge also rejected the argument that the requirement to show ID at the polls illegally creates two classes of people because there is no similar mandate for those who decide to vote early by mail. Silver said there is nothing inherently illegal about Arizona's setting up different practices and procedures for different types of voting.

Still unresolved is Perales' argument that the requirement violates the federal Voting Rights Act, which bars states from enacting regulations that have the effect of disproportionately discriminating against minority groups, even if that is not the intent of the law. Perales said Hispanics are less likely to have the kinds of documents necessary to register and vote.

Perales also contends the law unconstitutionally discriminates against naturalized citizens. She said that while they are presumed equal under the law, only those who are naturalized have to produce certain documents in person showing they have become citizens.

Her organization mounted a separate legal challenge to Proposition 200 shortly after the 2004 election, seeking to overturn another provision that denies certain public benefits to illegal immigrants. But a federal appeals court tossed the case, saying there was no evidence that anyone legally entitled to those benefits was in danger of being prosecuted for breaking the law.

This isn't the only outstanding lawsuit related to Proposition 200.

Randy Pullen convinced the state Court of Appeals earlier this year that he should be allowed to sue Gov. Janet Napolitano over how she is, or is not, enforcing the benefits portion of the initiative.

That lawsuit is based on the governor's decision that the measure makes only a few state services off limits to those not in the country illegally, basing that on a legal opinion from Attorney General Terry Goddard.

The appellate judges said the governor, as the state's chief executive, is required to ensure that all laws are obeyed, even those approved by voters. And they pointed out that Proposition 200 itself lets any Arizona resident go to court to argue that government agencies are illegally providing benefits to people.

That case eventually is expected to wind up before the state Supreme Court.