SPRINGFIELD - The state is sending some Illinois drivers letters telling them their license plates could be faulty. Secretary of State Jesse White's office is sending $60,000 worth of letters because in 2004 it was discovered that some plates issued in previous years could rust, making the plates' reflective coating ineffective.

The defect could cause police problems if they're trying to take down a plate number at night.

"It actually makes them very hard to read," said Ernie Dannenberger, director of vehicle services in White's office.

Now, license plates are made of aluminum and won't rust. But some issued in 2001 and 2002 were made of steel. People can change out problematic plates free of charge.

The office is sending out 160,000 letters, but many more drivers are potentially affected. Dannenberger said they're trying to see if the letters get people's attention.

The state has been putting notes about the plates on registration documents previously, but those hadn't gotten much attention.

Dannenberger said it was unclear how many plates had been changed out because of the defect because people get new ones for lots of different reasons.

But he said returns don't cost the state because the plates are covered by warrantee. In the early 2000s, license plates were manufactured both by Macon Resources in Decatur and Canada-based Waldale Manufacturing.