By David Shepardson

WASHINGTON (Reuters) -The union representing about 10,000 Southwest Airlines pilots told Reuters on Friday it supports an effort in Congress to extend an exemption from modern cockpit alerting requirements for the Boeing 737 MAX 7 and MAX 10 airplanes.

Boeing faces a December deadline to win approval from the Federal Aviation Administration (FAA) of the 737 MAX 7 and 10 variants, or it must meet new modern cockpit-alerting requirements that could significantly delay the plane’s entry into service.

Southwest Airlines Pilots Association President Capt. Casey Murray said in an interview Friday it made sense to have common alerts through the 737 family of airplanes.

“We believe in the interest of safety and commonality that it should be certified under the same rules,” Murray said, adding he supports the legislation’s goal to require future planes to have modern cockpit alerting systems.

On Wednesday, the Allied Pilots Association representing 15,000 American Airlines pilots said it opposes the extension for the Boeing MAX airplanes.

Both American and Southwest fly the MAX 8. Southwest has ordered MAX 7 planes.

Boeing argues it is safer to have one common 737 cockpit alerting system. “A consistent operational experience across an airplane family is an industry best practice that benefits flight crews and the flying public by enhancing safety and reducing risk,” Boeing said.

The requirements were adopted by Congress as part of certification reform passed after two fatal 737 MAX crashes killed 346 people and led to the bestselling plane’s 20-month grounding.

Reuters reported on Monday that Boeing does not anticipate winning regulatory approval for the MAX 10 before next summer, according to an FAA letter.

Last week, Senator Roger Wicker, the top Republican on the Commerce Committee, proposed extending the deadline for Boeing to win approval for the new variants until September 2024 and hopes to attach the proposal to an annual defense bill.

The Air Line Pilots Association, representing 65,000 airline pilots in North America, did not say Friday if it supports or opposes the extension.

(Reporting by David ShepardsonEditing by Chris Reese and Nick Zieminski)