The American Civil Liberties Union is leading the call for an end to the way the Illinois State Police conducts some routine traffic stops. The organization says officers unfairly search minorities.

The ACLU points to a new study by Northwestern University. In it, researchers find that state officers ask to search the cars of minorities three times more often than the cars of whites. The suspects don't have to agree to the search, but frequently allow it. Of those who are searched, it's whites who are typically caught with something illegal. Harvey Grossman, with the ACLU, says the practice victimizes minorities.

GROSSMAN: When we put in play these kinds of practices that year after year, disproportionately and unfairly, unjustifiably impact our minority drivers, we have to simply put a halt to them.

The governor's office did not comment on Grossman's call to ban the voluntary searches. In a written statement, the state police point out the number of such searches has gone down over the past couple years and that the department has no tolerance for officers who use bias in their policing.