Washington: U.S. Transportation Secretary Sean Duffy is expected to order scheduled air traffic cut by 10% at 40 major airports starting Friday without a deal to end the government shutdown, sources familiar with the situation said.

The shutdown has forced 13,000 air traffic controllers and 50,000 Transportation Security Administration officers to work without pay, snarling tens of thousands of flights.

Duffy had warned on Tuesday that if the federal government shutdown continued another week, it could lead to “mass chaos” and force him to close some of the national airspace to air traffic, a drastic move that could upend American aviation.

Airlines have repeatedly urged an end to the shutdown, citing aviation safety risks.

Shares of major airlines, including United AirlinesUAL.Oand A

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