The California Department of Motor Vehicles announced Wednesday that more than 1 million illegal immigrants have obtained driver’s licenses under a state law that took effect a little more than three years ago.

Assembly Bill 60, which took effect in Jan. 2015, allows illegal immigrants to apply for California driver’s licenses if they provide proof of residence in the state and some form of identification, which can be a foreign passport or ID card. Applicants must pass both a written exam and a behind-the-wheel test in order to obtain the special driver’s licenses. The written exam can be taken in Spanish.

The licenses may not be used for federal purposes, including boarding an airplane. California is one of at about a dozen states that allow illegal immigrants to obtain driver’s licenses.

Following the passage of the law, the California DMV estimated about 1.5 million people would apply for the special driver’s licenses in the coming years. As of March 30, slightly more than 1 million people have obtained the driver’s licenses.

Luis Alejo, a former assemblyman who authored AB 60, stated on Twitter that the legislation has proved to be a huge success.

“1 million immigrants have a driver’s license today under my AB 60! They are tested, licensed and insured! They can now drive to work, take their kids to school or go see the doctor without fear their cars will be impounded! A huge CA success story for immigrants, our roads and our economy!” Alejo wrote.

Critics have said the driver’s licenses legitimize illegal immigrants and could be used for voter fraud.