U.S. Department of Transportation Secretary Sean Duffy on Thursday raised concerns about air traffic controllers taking on second jobs to pay their bills during the government shutdown.

The government shutdown entered day 24 Friday as fears mounted that the impacts of the funding lapse may soon start to bite.

Nearly 5,000 flights within, into or out of the U.S. were delayed Thursday, while more than 700 were canceled, according to flight-tracking site FlightAware.