The Air Line Pilots Association (ALPA) is warning President Donald Trump that a prolonged shutdown of the US government will put the lives of air travellers at risk, Newsweek reports.

“The disruptions being caused by the shutdown are threatening the safe operations of [the US air transportation] network,” wrote ALPA President Captain Joe DePete in a January 2 letter to Trump.

DePete noted that the US Department of Transportation and Department of Homeland Security have both regulatory and service roles, and, “When any of their responsibilities are placed on pause due to a shutdown there are safety, security and efficiency gaps that immediately emerge.”

Federal workers being compelled to stay on the job without pay, including air-traffic controllers and security staff, also are “facing significant financial hardship” due to the shutdown, initiated by Trump to try to pressure Democratic lawmakers to fund a multibillion-dollar wall along the southern border of the US, DePete wrote.

The shutdown is fast approaching the benchmark of the longest in history, 21 days, with little sign of a resolution in sight.