The US government shutdown is a threat to the safety, security, and efficiency of America's airspace.

The Air Line Pilots Association International sent a letter to President Donald Trump on Wednesday urging him to end the shutdown.

ALPA is a union that a represents 61,000 pilots working for a variety of airlines, including Delta, United, JetBlue, and Alaska.

The effects of the latest government shutdown are being felt across the US.

The air-transport system on which America depends is also feeling the pinch. On Wednesday, the Air Line Pilots Association International (ALPA) sent a letter to President Donald Trump urging him to end the shutdown.

"I am writing to urge you to take the necessary steps to immediately end the shutdown of government agencies that is adversely affecting the safety, security, and efficiency of our national airspace system," Captain Joe DePete, the president of the ALPA, said in the letter.

The union, which represents 61,000 pilots flying for airlines such as Delta, United, JetBlue, and Alaska Air, is concerned that the lack of working inspectors and regulators could compromise the safety of air travel in the US.

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"At the Federal Aviation Administration (FAA) there are fewer safety inspectors than are needed in order to ensure the air traffic control infrastructure is performing at its peak levels of performance," DePete said. "There are also airline and aircraft manufacturing oversight activities that either stop or are significantly reduced."

"These safety and oversight inspections will potentially allow for the introduction of safety issues that put passengers and airline crews at risk," the union leader went on to say.

In addition, ALPA expressed concern that a prolonged shutdown will cause long-term financial harm to personnel who are working unpaid.

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"The air traffic controllers, airspace system maintenance personnel, and the airline passenger security workforce are being asked to work unpaid," DePete said. "They are dutifully providing safety of life services while facing increasingly difficult financial pressures to provide for those dependent on their paycheck."

The National Air Traffic Controllers Association last week voiced similar concerns over understaffed and unpaid air-traffic-control centers.