By David Shepardson

WASHINGTON, March 15 (Reuters) - The CEOs of major U.S. airlines urged Congress on Sunday to move quickly to end a 29-day partial government shutdown that has forced 50,000 airport security officers to work without pay, warning it could further disrupt U.S. air travel.

Absences by Transportation Security Administration officers have ​already disrupted travel at some major airports over the last week, raising alarm as the busy spring break travel season continues.

"Too many travelers are having to wait in extraordinarily long - and painfully slow - lines at checkpoints," the CEOs of American Airlines AAL.O, United Airlines UAL.O, Delta Air Lines DAL.N, Southwest Airlines LUV.N, JetBlue Airways JBLU.O, Alaska Air ALK.N and others wrote in an open letter to Congress.

"First, leaders should immediately come together to reach an agreement to fund the Department of Homeland Security. Then they need to act so this problem never happens again," they added.

Last fall, a 43-day government shutdown led to widespread flight disruptions and the FAA ordered a 10% flight cut at major airports. "Once again air travel is the political football amid another government shutdown," the CEOs wrote.

The group of airline executives - which also includes senior executives at cargo carriers FedEx FDX.N, UPS UPS.N and Atlas Air - called for legislation to ensure during future government shutdowns all critical government aviation personnel are paid.

Senators from both parties failed on Thursday in competing efforts ​to fund the TSA, which said last week that ​more than 300 officers have quit since the ‌shutdown ⁠began.

The Homeland Security Department's funding lapsed on February 13 after Congress failed to reach a deal ​on immigration enforcement reforms demanded by Democrats.

Airlines are expecting a ​record-breaking spring ⁠travel period, with 171 million passengers expected to fly, up 4% from the same two-month period last year.

Last week, some airports like Houston Hobby and New Orleans reported security lines exceeding two hours as ​TSA absences rose, while on Saturday, Newark said it was experiencing higher-than-normal delays.

"Americans - who live in your districts and home states - are tired of long lines at airports, travel delays and flight cancellations caused by shutdown after shutdown," the CEOs wrote.

Some airports have closed some security checkpoints and others are working to raise money to help TSA workers buy food or other essentials as they go without pay.

(Reporting by David Shepardson; Editing by Jamie Freed)

((David.Shepardson@thomsonreuters.com; 2028988324;))