Florida Sen. Marco Rubio and his Democratic opponent Rep. Patrick Murphy are sparring about their positions on gun law reform in the wake of the Orlando nightclub massacre.

Rubio famously jumped into the race, largely citing the shootings at the Pulse nightclub in June, after saying he would not run for re-election.

Rubio introduced legislation this week that, among other provisions, would require the FBI director and Joint Terrorism Task Force to be notified if the subject of a federal terrorism investigation in the last 10 years tries to obtain a firearm. In addition, the U.S. attorney general can delay the transfer for up to three days and file a petition to stop it.

“This bill would achieve everyone’s goal of making it harder for suspected terrorists to buy guns,” Rubio said in a statement. “And do so without violating the due process and Second Amendment rights of innocent, law-abiding Americans.”

Murphy’s campaign called the bill a “transparent attempt to paper over relentless opposition to legislation that prevents gun violence.”