A small percentage of domestic flights were canceled on Friday, but Transportation Secretary Sean Duffy said the reductions, which were already going to increase next week, could sharply rise by the holidays if the shutdown continued.

Follow our coverage from Republic reporters of the effect of the federal government shutdown on air travel and Phoenix Sky Harbor flights.

As many as 1,800 flights could be affected on Friday alone, according to Cirium, an aviation-data provider. The final figure will depend on which airports are targeted. The FAA estimates that it handles an average of more than 44,000 flights a day.

Travelers across the U.S. are facing potential chaos as a government shutdown threatens to disrupt flights nationwide