US air travellers are experiencing a second day of flight delays and cancellations, as the government shutdown causes a worsening shortage of air traffic controllers. On Tuesday evening, the flight delays hit even more airports, with the cities of Nashville, Dallas, Chicago and Newark especially affected. On Monday, air traffic control at the Hollywood Burbank Airport in California was unmanned for nearly six hours and remotely managed due to staffing shortages. Transportation Secretary Sean Duffy said some air traffic controllers are calling in sick as the shutdown, now in its seventh day, adds stress on workers. He estimated that staffing has at times dropped to 50% in some areas. Meanwhile, The Trump administration is warning federal workers furloughed in the government shutdown that they may not get back pay once the funding impasse ends, which some lawmakers are decrying as illegal. On Tuesday, Trump told reporters that back pay "depends on who we're talking about" and that some workers "don't deserve to be taken care of".