Colorado officials claim they accidentally sent approximately 30,000 postcards last month to noncitizens instructing them how they could register to vote.

First reported by Colorado Public Radio News, Democratic Secretary of State Jena Griswold’s office said department employees had sent the postcards on Sept. 27 after comparing a list of 102,000 names provided by the Electronic Registration Information Center, a nonprofit organization aiming to improve U.S. voter rolls and advocating residents to vote.

“The Department has become aware that approximately 30,000 EBU [Eligible But Unregistered] postcard mailers were incorrectly sent to ineligible Coloradans,” a spokesperson for the Colorado Secretary of State’s Office told local media. “The office is undertaking an internal review of the incident and will take any corrective action that is warranted.”

Griswold insisted noncitizens would not be allowed to register to vote.

The postcards, which the office printed in English and Spanish, read, “A message from Colorado Secretary of State Jena Griswold . . . Our records indicate that you or your household may be eligible to vote, but do not appear to be registered at your current address.”

The mailers did include that to vote that residents must be 18 years old by Election Day, a United States citizen, and a Colorado resident for at least 22 days before the upcoming election, according to Colorado Public Radio News.

Griswold’s office said they plan on sending out correction mailers to the noncitizens, “reminding them that only those that meet the above requirements are eligible to register.”

According to local media, while the office had compared the list of potential unregistered voters to local DMV records, the data had included noncitizen drivers with Colorado driver’s licenses which the state issues for noncitizens to drive legally.

The National Council on State Legislatures website shows Colorado as one of at least 17 states, along with the District of Columbia, that issue driver’s licenses to non-U.S. citizens.

However, the system did not distinguish their eligibility to vote.

Sean Morales-Doyle, director of the Voting Rights Program at the Brennan Center for Justice, told The Journal that the system making a mistake indicates it works.

“It should show, first of all, that mistakes can happen, but secondly that there are checks in place to make sure mistakes don’t result in disaster,” Morales-Doyle said. “It’s not good this happened. It appears to be a case of human error and a database error and not some conspiracy, which I think some critics would seize on.”

Morales-Doyle added that very few noncitizens have attempted to register in the U.S. for fear of the consequences, including deportation.

Colorado’s Republican Party chair, Kristi Burton Brown, condemned Griswold for the error, saying in a Monday statement to Fox News that “Jena Griswold continues to make easily avoidable errors just before ballots go out.”

Griswold is up for reelection in the November midterms, where she will face Republican Pam Anderson, the head of the state’s county clerks association.