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Airports across the country were starting to buckle Monday under the strain of the partial government shutdown as a rising absentee rate among federal transportation security officers, who are not being paid, led to the closing of checkpoints and increased wait times for travelers.

At George Bush Intercontinental Airport in Houston, the checkpoint in Terminal B remained closed at midday because of a shortage of screening agents, Patrick Trahan, a spokesman for the Houston Airport System, said. On Sunday, Bush Intercontinental became the second big airport to close a main passenger screening portal because of abnormally high absenteeism since the shutdown began on Dec. 22.

On Monday, about one of every 13 screeners nationwide failed to report for work, compared with about one out of 30 a year ago, said Michael Bilello, a spokesman for the Transportation Security Administration. Mr. Bilello said Washington-Dulles International and Hartsfield-Jackson Atlanta International airports were “exercising contingency plans due to call-outs.”

The T.S.A.’s 51,000 employees were ordered to work without pay during the shutdown. On Friday, they saw their first missed paycheck, a lapse that travel industry officials worried would cause more of them to stay home or quit their jobs, leading to more disruptions for travelers.