US President Donald Trump has ordered the country's air traffic controllers to immediately return to work amid warnings domestic flights could "slow to a trickle".

In a post on Truth Social, he said those controllers who refuse to work would face penalties while promising bonuses for those who have worked during the government shutdown.

"Anyone who doesn't will be substantially 'docked.' For those Air Traffic Controllers who were GREAT PATRIOTS, and didn't take ANY TIME OFF for the 'Democrat Shutdown Hoax,' I will be recommending a BONUS of $10,000 per person for distinguished service to our Country," Trump wrote.

He also posted those who didn't work "will have a negative mark, at least in my mind, against your record".

US airlines cancelled more than 2700 domestic flights on Sunday a

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