U.S. AIRPORTS — Major U.S. airlines are allowing passengers to cancel or rebook tickets without charge as security screening lines stretch for hours at airports during the partial federal government shutdown. Allegiant Air, Delta Air Lines and United Airlines have issued travel waivers for affected passengers.

At Houston's George Bush Intercontinental Airport, passengers reported waiting five hours to be screened, leading to missed flights. Passenger Summer Martinez missed three flights due to long lines and hoped her fourth attempt to fly to Tulsa, Oklahoma would be successful.

Allegiant Air has issued a travel guarantee that lets customers traveling during the partial government shutdown change or cancel their itineraries at no additional cost. For a limited time, the airline is offering eligible fliers no change fees and the option to cancel a flight for a refund. Customers must contact Allegiant Air's customer service team directly by phone, chat, text, or email to change or cancel a flight. The airline encourages passengers to allow for extra time at airport security screening lines and urges customers to check their local airport's website or social media channels for projected TSA wait times.

Delta Air Lines' waiver applies specifically to Hartsfield-Jackson Atlanta International Airport, which advises passengers to allow at least four hours for domestic and international flight security screening. Passengers with plans to travel on Tuesday may rebook their Delta Air Lines trips to fly on or before March 30 without additional charges. Delta will waive any fare differences for passengers who rebook tickets in the same cabin of service they originally selected.

United Airlines issued a special waiver for travelers flying to or from George Bush Intercontinental Airport in Houston, where passengers have faced wait times of up to six hours due to TSA worker absences. United passengers with original travel dates on March 23 and 24 may reschedule trips departing on or before March 31 with the airline waiving all change fees and fare differences. Rescheduled flights under United's waiver must depart on or before March 31 and remain in the same cabin between the same origin and destination cities as originally booked.

"It's probably about time they started doing this, given the chaos at key hubs like Houston and Atlanta. It appears airlines are facing the fact that there doesn't appear to be an end in sight to this anytime soon," said Eric Rosen, director of content.

Some passengers struggle to determine how early they should arrive at airports before a flight due to conflicting information from airports and airlines. TSA officers are quitting in large numbers as they work without pay for a sixth consecutive week. Lawmakers have not passed a spending bill to fund the Department of Homeland Security, which oversees the Transportation Security Administration.