An additional 2,000 US flights were canceled Monday as President Donald Trump threatened to dock pay for air traffic controllers who called in sick during the government shutdown.

After Trump ripped absent aviation workers as unpatriotic, the National Air Traffic Controllers Association (NATCA) labor union hailed members working without pay as "unsung heroes" in a statement that called for Congress to immediately end the shutdown.

"Enough is enough," the union said.

The back-and-forth highlights the mounting strain on the aviation industry as the record-breaking shutdown hit day 41, though a compromise bill advancing in Congress was raising hopes of an imminent resolution.

The air traffic control system was already under strain prior to the shutdown due to understaffing, and is facing

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