Forty of the country’s busiest airports have been affected by the domestic flight cancellations. Here is the list.

Mass cancellations of flights in the United States are causing havoc for travellers after the government ordered a reduction in the flight schedule due to a lack of air traffic controllers.

The reduced flight schedule, set to begin on Friday, comes as the US continues with its longest-ever government shutdown, which began on October 1, after Congress was unable to agree on a federal funding bill.

On Thursday night, the Federal Aviation Administration (FAA) announced a phased-in reduction plan, which sets out that airlines must cut 4 percent of domestic flights from 6am EST (11:00 GMT) on Friday and gradually increase to 10 percent by November 14.

So far, no international flights have been affected by the planned cancellations.

According to an estimate by the aviation analytics firm Cirium, about 1,800 flights are being cancelled – a reduction of 268,000 seats.

Here’s what we know about the cancellations:

Why are flights being cancelled in the US?

Since the October 1 government shutdown, now the longest in history, there has been no sign of the Republicans and Democrats ending their standoff over healthcare funding and agreeing on a new funding bill. Hundreds of thousands of federal workers, including air traffic controllers, have been furloughed or are working unpaid.

While federal workers have received back pay following the end of p