Some immigration reformers are quick to call it another sign of fraud, but state officials say it's too early to tell why more than 40 percent of the expiration notices mailed to state ID card holders are being returned as undeliverable.

Nearly 30,000 of the 74,000 notices sent to people holding a state ID card have been returned. The cards, issued to people who don't have a Social Security card, are expiring under a controversial immigrant policy bill approved earlier this year by the Legislature.

An immigration policy critic says the heavy return margin is just another indication of people using the state ID system as a cover. And the bill's sponsor says it is further evidence the legislation was needed to put a stop to it.

State Department of Public Safety spokesman Lt. Doug McCleve said the state will be taking "a very close look" at why the notices are being returned. "We need to look at that and determine why it's happening and if there's any criminal responsibility."

The legislation, SB227, repealed a 1999 law allowing an undocumented immigrant to obtain a Utah driver's license using an individual tax identification number issued by the Internal Revenue Service to those who don't qualify for Social Security numbers.

The bill creates a driving privilege card that can't be used for identification.

Some 61,000 drivers' licenses issued to people with tax numbers will expire on their first birthday after July 1, McCleve said.

The notices were sent out to inform those with state ID cards or drivers' licenses but no Social Security numbers of the deadline.

So far, some 5,280 driving privilege cards have been issued since the state stopped issuing state IDs and drivers' licenses to undocumented immigrants in early March, McCleve said.

A separate piece of legislation also makes the driving privilege card available to legal residents who don't have a work purpose, such as those with student visas, on July 1.

Sponsoring Sen. Curt Bramble, R-Provo, said he wouldn't be surprised if the public safety investigation has results mirroring a legislative audit. That audit showed several licenses being linked to the same or similar addresses.

Using information from an Immigration and Customs Enforcement investigation, the audit found addresses appear to be used by " 'contractors' who charge a fee for helping undocumented aliens obtain a Utah driver's license." The audit also suggested that 14 people who appeared to be undocumented had voted in an election.