New York, New York - President Donald Trump threatened Monday to dock the pay of air traffic controllers he accused of shirking their "patriotic" duty, while their union decried being used as "political pawns" during the government shutdown.

The statements highlighted the mounting strains on the aviation industry as the record-long shutdown hit day 41, though a compromise bill advancing in Congress was raising hopes of an imminent resolution.

Thousands more trips involving US airports were canceled or delayed Monday after nearly 3,000 were cut a day earlier, according to tracking website FlightAware.

The Trump administration last week ordered 10-percent reductions in flights at dozens of airports, including some of the nation's busiest, due to concerns that staffing strains could threaten safety.

Air traffic controllers, who are already in short supply in the US, have been working without pay during the shutdown, leading some to call in sick.

Trump took to social media on Monday to slam the absenteeism as unpatriotic, threatening that those who do not return to work "will be substantially 'docked.'"

"All Air Traffic Controllers must get back to work, NOW!!!" he demanded on his Truth Social platform.

Trump said he was recommending a bonus of $10,000 to the "GREAT PATRIOTS" who did not take time off during the shutdown.

His statement was posted just as a press conference was concluding with the National Air Traffic Controllers Association (NATCA), organized to mark the second consecutive zero-dollar paycheck for its members.

"Enough is enough," said NATCA president Nick Daniels. He called an emerging deal in Congress a "right step in the right direction."

"Air traffic controllers should not be the political pawn during a government shutdown," said Daniels, who has spoken in increasingly dire terms since federal funding first lapsed on October 1.

NATCA did not immediately respond to a request for comment on Trump's remarks.

Democratic congressman Rick Larsen called Trump's comments "nuts."

"The women and men working long hours in air traffic control towers to keep the aviation system running deserve our thanks and appreciation, not unhinged attacks on their patriotism," said the Washington representative.