More than 400 passengers missed their flights on one night thanks to TSA security lines of up to three hours on Sunday at Chicago O'Hare International Airport, as the growing crisis at the agency causes travel chaos across the nation. Dozens of the passengers were forced to sleep on cots at the nation's third-busiest airport Sunday night, because extremely long security lines kept them from making their flights. And the lines didn't improve Monday morning, as the lines wound back and forth through the hallways during the early morning rush when passengers were told to expect waits of as long as three hours for international flights. Even in the afternoon, wait times at the nation's busiest hours were more than 30 minutes long. The TSA last week warned travelers to expect delays across the nation after they cut their staff numbers and the number of travelers increases. At O'Hare, the nation's third-busiest airport, some 4,000 passengers have missed flights since February due to an understaffed TSA and record flight sales, according to American Airlines. The TSA has pledged to add 800 new security screeners by June, but the union that represents these workers says 6,000 new hires need to be made to speed up the screening process. The reason for the shortage of TSA workers is due to federal budget cuts. In the meantime, transportation officials are urging passengers to arrive two hours before domestic flights and three hours before international flights to give them enough time to make it through the line. But like those camping out in the airport Sunday night, even following these rules sometimes fails. U.S. Senator Chuck Schumer, of New York, has also proposed increasing the amount of security dogs, which he says could cut wait times in half. Last week, Homeland Security Director Jeh Johnson asked fliers to be patient as the government tackles the TSA employee shortage. 'Our job is to keep the American people safe,' Johnson told reporters at a news conference. 'We're not going to compromise aviation security in the face of this.' The TSA cut its airport screener staff by 10 per cent in the past three years with the assumption the PreCheck program would speed up the process. But the program requires an $85 to $100 fee every five years, and applicants need to pass an interview before they are allowed to go through faster lanes, where passengers don't have to take off their shoes or remove laptops and liquids from their bags. Last week, Congress agreed to shift $34 million in TSA funding forward, allowing the agency to pay overtime to its existing staff. The money will also go towards hiring 768 screeners by June 15 to bring numbers up to the congressionally mandated ceiling of 42,525. With fewer staff, stricter security procedures, and a record number of fliers, the perfect storm has been brewing for months. Airlines have been warning customers to arrive at the airport two hours in advance, but with summer travel season approaching even that might not be enough. Johnson said the TSA is working with airlines to enforce limits on carry-on bags and their size.