DENVER (AP) — A Denver federal judge is hearing arguments on a lawsuit by Colorado sheriffs seeking to block new limits on ammunition magazines.

District Judge Marcia Krieger is being asked at a Wednesday hearing to grant a preliminary injunction on a state law that bans magazines with more than 15 rounds. The law took effect July 1, along with universal background checks on firearm purchases. Both passed in response to mass shootings in Colorado and Connecticut last year.

The sheriffs say the law violates the Second Amendment. They also contend it's vague because magazines can be converted to hold more rounds.