WASHINGTON -- Two senior U.S. Senate Democrats urged Attorney General Merrick Garland on Monday to investigate and prosecute unruly air passengers in the face of a rising number of incidents onboard airplanes.

Senate Majority Whip Dick Durbin and Commerce Committee chair Maria Cantwell called on the Justice Department and Federal Aviation Administration (FAA) to coordinate efforts to "ensure qualifying passenger behavior is criminally prosecuted."

"Civil penalties alone are failing to deter criminal activity by airline passengers," Durbin and Cantwell wrote in the .

The FAA and Justice Department did not immediately comment.

In June, a group representing major U.S. airlines such as American Airlines, Delta Air Lines and United Airlines, and aviation unions also asked Garland to prosecute the growing number of disruptive and violent air passengers.

The letter from Airlines for America said the "incidents pose a safety and security threat to our passengers and employees, and we respectfully request the (Justice Department) commit to the full and public prosecution of onboard acts of violence."

To date this year, there have been 4,284 reports of , including 3,123 that were mask-related. The FAA has initiated enforcement actions in 154 cases, issuing more than $1 million in proposed fines.

FAA Administrator Steve Dickson imposed in January a zero-tolerance order on passenger disturbances aboard airplanes after supporters of former U.S. President Donald Trump were disruptive on flights around the Jan. 6 U.S. Capitol attack. That policy will extend until at least as long as federal mask rules on airplanes are in place, which were extended last month into mid-January 2022.

"It is critical that DOJ direct federal law enforcement agents and prosecutors to use these authorities to fully investigate reported incidents on aircraft, and, when supported by the evidence, prosecute those who are criminally responsible," Durbin and Cantwell's letter to Garland said.

Separately, the House Transportation and Infrastructure Committee will hold a hearing on Thursday that will include aviation union and other industry officials, titled "Disruption in the Skies: The Surge in Air Rage and its Effects on Workers, Airlines, and Airports."

Reporting by David Shepardson; Editing by Karishma Singh