About 95,000 people who are not U.S. citizens could be improperly registered to vote in Texas, and about 58,000 of those cast a ballot “in one or more Texas elections,” according to state officials.

Texas Secretary of State David Whitley said Friday his office and the Department of Public Safety conducted a yearlong investigation into Texas voter rolls to identify registered voters who may not have U.S. citizenship, the Austin American-Statesman reported.

Those names were passed on to the Texas attorney general, who vowed to investigate possible illegal activity and prosecute those who have broken the law. Voting in a U.S. election when not eligible is a felony with a prison term of two to 20 years.

“Nothing is more vital to preserving our Constitution than the integrity of our voting process, and my office will do everything within its abilities to solidify trust in every election in the state of Texas,” Attorney General Ken Paxton said.

Those suspected of not being U.S. citizens will have 30 days to provide proof or risk being purged from the voter rolls.