President Barack Obama’s Department of Homeland Security rejected California’s proposed design for driver’s licenses that will be awarded to illegal immigrants in 2015 because it would be nearly impossible for federal officials to distinguish the licenses from those given to legal residents.

According to the Los Angeles Times, the federal Real ID Act requires markings on licenses “to allow Federal officials to quickly determine whether a license or identification card may be acceptable for official purposes” including “accessing Federal facilities, boarding federally regulated commercial aircraft, or entering nuclear power plants.”

Illegal immigrants will be able to get licenses in 2015 because of legislation signed by Gov. Jerry Brown (D) in 2013. An estimated 1.4 illegal immigrants are expected to apply for the licenses in the next three years.

The Department of Homeland Security informed the California Department of Motor Vehicles (DMV) on May 1 of its decision and, according to the Times, the federal government wants the licenses for illegal immigrants to clearly state on the front “that it is not acceptable for official federal purposes” and also be in a different color than regular licenses. 

The Times notes that “the current design does not differ from other California licenses except for a subtle mark on the front and a disclaimer on the back in small print: ‘This card is not acceptable for official federal purposes.'”

Critics of California’s licenses for illegal immigrants have cited national security concerns, but illegal immigrant activists from the Latino Legislative Caucus wrote to Department of Homeland Security’s Jeh Johnson to protest the markings that they consider to “be a kind of scarlet letter.”

Sen. Ricardo Lara (D-Bell Gardens), the Chairman of the Latino Caucus, reportedly said the decision “is disappointing and troubling.”

A spokesman for the California Department of Motor Vehicles told the Times that the DMV will continue to work vigorously with lawmakers, affected communities, and federal officials to design a license that complies with federal law and allows over a million undocumented California residents to drive legally and safely on state roads.”