DENVER (CBS4) – Colorado’s Department of Motor Vehicles mistakenly issued U.S. citizen driver’s licenses to 524 non-citizens, including some illegal immigrants, CBS4 has learned.

The licenses look like those given to state residents. The DMV blamed a software problem at a contractor, who is working with DMV to retrieve the licenses and re-issue correct IDs.

The licenses were mailed at the beginning of September. The contractor said it learned on Sept. 8 that the printing error occurred Aug. 8.

“What happened is there was a software update error on the part of the vendor,” said Director of Dept. of Revenue Barbara Brohl.

The DMV said Friday that drivers left its offices with correct temporary licenses, but the contractor later mailed the incorrect permanent licenses.

The contractor emailed the recipients of the licenses on Friday to ask for the licenses back. The contractor will issue the correct credential, it said, along with a gift card to compensate the individuals affected.

Colorado lawmakers passed a law that took effect Aug. 1 that grants licenses to non-citizens to improve public safety by making sure that all drivers in the state, regardless of their status, are licensed. They are marked, however, with a black strip that reads “Not Valid For Federal Identification, Voting or Public Benefit Purposes.”

“If they don’t send the licenses back we’ll go into Plan B and we’ll figure that out but we will be getting them all back,” said Brohl.

When the DMV announced it would issue appointments to non-citizens to receive licenses, calls and online orders deluged its offices. Tens of thousands reportedly contacted the DMV to register for the new ID, apparently clogging the system. On July 1, the first day it began offering appointments, the DMV scheduled 823, more than 100 an hour during office hours.

“The worry that I have, now that I’ve learned about this, is people could show up to register and vote the same day and their driver’s licenses don’t have that indicator,” said Secretary of State Scott Gessler.

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Those in the country illegally or without a Social Security number are eligible for the license if they prove they live in Colorado and pay taxes. Those in the country illegally must prove they have applied for citizenship.

“It puts us in a bind to scramble to get that thing fixed,” said Gessler.

“It is my plan to get these back and to get them back before the election,” said Brohl.

Gabriela Flora, an immigration community advocate who lobbied for the law, said in July the DMV expected 45,000 applicants the first year.