In a prepared statement to CNN's Lou Dobbs, Cannon said, "It is ludicrous to suggest that my campaign would condone voting by non-citizens or contributions by foreign nationals."

Throckmorton said he was worried Cannon might try to get illegals to register.

Meanwhile, Naccarato strongly denied voter fraud is a problem in Utah.

"There is this misconception that people are going into driver's license offices and illegally registering to vote," the elections director said. "It's just not happening."

A leader in Utah's Latino community said the challenge could backfire.

ProjectUSA and other out-of-state groups considered "anti-immigration" by Latinos have "fired up our base" of about 60,000 registered Latino voters, said Tony Yapias, director of the State Office of Hispanic Affairs.

"The irony," he said, "is the Latinos have woken up, both in leadership and influence."

The potential voter challenge seems to confirm the Wall Street Journal's observation that, nationally, "extra special attention is being paid to a GOP House primary in Utah" because of the immigration issue.

The paper's lead editorial said Throckmorton, ProjectUSA and other groups are running a campaign based on fear of foreigners.

The intraparty confrontation "comes courtesy of deep-pocketed restrictionists campaigning on behalf of his opponent, who is running hard on xenophobia," the paper wrote.

The Journal's opinion is that a division over immigration is growing among Republicans in Congress because groups trying to restrict immigration have targeted several congressmen.

Driver's license and voter registration databases are separate, Naccarato said. Citizens can check a box to register to vote when they fill out a driver's license form, but they aren't registered until a state or county clerk confirms their eligibility.

A pre-election voter challenge must be filed in the form of a written affidavit listing a voter's name and the reason for the challenge, Naccarato said. No bulk challenge has ever been attempted.

Voters who show up at the polls and find out they have been challenged can still vote on a provisional ballot, which is marked separately from the other ballots, if they fill out a form similar to an original voter registration.

She suggested voters bring proof of identification and residency to the polls on Tuesday.

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E-mail: dbulkeley@desnews.com; twalch@desnews.com