Air transport workers warned the five-week-old US government shutdown could cause US commercial aviation to collapse as they planned a protest Thursday in the US capital's Reagan Washington National Airport.

"We have a growing concern for the safety and security of our members, our airlines, and the traveling public due to the government shutdown," leaders of the National Air Traffic Controllers Association, Air Line Pilots Association and Association of Flight Attendants said in a strong statement.

"In our risk averse industry, we cannot even calculate the level of risk currently at play, nor predict the point at which the entire system will break. It is unprecedented," they said.

With a divided Congress expected to prove unable to pass either of two bills aimed at ending the shutdown in votes scheduled Thursday, the three unions noted that air traffic controllers, transportation security officers, safety inspectors and air marshals have all been working for over a month without pay.

"Staffing in our air traffic control facilities is already at a 30-year low and controllers are only able to maintain the system's efficiency and capacity by working overtime."

At some of the busiest airports, controllers are working 10-hour days and six-day workweeks, all without paychecks.

They also pointed to the lengthening of passenger inspection times in airports due to an increasing number of workers for the Transportation Safety Administration not showing up.

Many TSA workers have sought other jobs rather than continue to work unpaid for TSA.

With President Donald Trump and Democrats in Congress appearing no closer to a deal to end the shutdown, on Thursday morning Democratic legislators were planning to join the unions' protest at the Washington airport.

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