The partial government shutdown rippled through the U.S. transportation system Monday as staffing issues closed a security checkpoint at Houston’s largest airport and the world’s biggest hub in Atlanta suffered unusually long lines.

The issues at several airports stem largely from a shortage of Transportation Security Administration staff, who have been calling in to say they wouldn’t be showing up for work in recent weeks and whose absences accelerated over the weekend.

Houston’s George Bush Intercontinental Airport said it didn’t have enough TSA staff to work all checkpoints and said its Terminal B screening point would remain closed Monday after shutting down Sunday.

Meanwhile Atlanta’s Hartsfield-Jackson International Airport, the world’s busiest airport by passenger traffic, reported delays of more than an hour at checkpoints early Monday, though by mid-morning most had been reduced to normal levels.

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Many TSA employees, who are responsible for screening passengers and scanning bags, are among the 420,000 essential government employees still working but not receiving pay during the partial government shutdown that is now the longest on record.

The TSA’s unplanned absence rate hovered at around 5 percent the week leading up to Friday, when the agency’s workers missed their first paycheck. On Monday, the rate was 7.6 percent, up from 3.2 percent on the same day a year ago.

The TSA said Monday it would shift screeners around the U.S. to respond to shortages that crop up, with the first deployments to Atlanta and Houston.

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On Monday, Democrats in Colorado’s congressional delegation held a news conference at Denver International Airport.

Sen. Michael Bennet and U.S. Reps. Diana DeGette of Denver, Ed Perlmutter of Golden, Joe Neguse of Fort Collins, and Jason Crow of Aurora called for an end to the longest shutdown in American history.

“This is a travesty,” Bennet said. “There’s no reason why this government should be shut down over the president’s temper tantrum. It’s now been 24 days.

“(Sen. Majority Leader) Mitch McConnell should put a bill on the floor that the Senate has voted for unanimously, and reopen the government,” the Colorado Democrat added, “and if the president vetoes it, the House would override that veto tomorrow – and the U.S. Senate would override it the day after that.”

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U.S. Rep. Diana DeGette, D-Denver, said that legislation to reopen the government has already passed both the House and the Senate at different times. She too called on McConnell to call for a vote.

“It’s getting to the point where it’s way beyond the issue of Donald Trump and his wall, it’s getting to the point of the safety of every single passenger who’s flying through this airport,” DeGette said.

Republican lawmakers did not attend the news conference.

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DIA officials said Monday that they have not yet encountered the delays seen at Atlanta and Houston.

Contacted on Monday about the shutdown, Greg Phillips, director of aviation at Colorado Springs Airport, said in an email that “So far, we still don’t see any checkpoint impacts at COS, but I’m not sure how much longer that can last. This is hard on them, as you know.”

At Houston, the airport said passengers scheduled to depart from Terminal B, which is closed, will instead go through security at checkpoints located in other terminals and then walk or take a tram to their gates. Flights will still depart from Terminal B, one of five at the airport, which is exclusively used by United Airlines. United didn’t have an immediate comment.

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In Atlanta, the TSA said it was working with the airport to make adjustments and that the airport was experiencing high passenger volumes, contributing to the waits.

“Lines are long this morning, but they usually are on Mondays,” said Elise Durham, an airport spokeswoman. “We are down a few security lines, but things are moving pretty efficiently.” Delta Air Lines Inc., its largest operator, didn’t immediately respond to a request for comment on the delays.

The developments raise concerns that travelers will begin to feel the impact of the government shutdown more acutely as it stretches on.

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“Airports in certain locations will begin exercising consolidation options during peak periods,” the TSA said. “These decisions will be made at the local level.”

A handful of large U.S. airports, including San Francisco International, outsource security screening to private contractors under a program overseen by the TSA. A spokesman for the San Francisco facility said its screeners continue to be paid.

A spokesman for Miami International Airport said operations returned to normal Monday, after it had to shut one of its concourses early on Saturday and Sunday.

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Hydrick Thomas, president of the TSA Council at the American Federation of Government Employees, said in a statement last week that some TSA workers have already quit and many others are considering it.

The TSA has said nearly all passengers have cleared security in under a half-hour throughout the shutdown and that security hasn’t been compromised. Airports in Chicago, Boston, Phoenix, Minneapolis, Orlando, and elsewhere have said their operations were normal over the weekend.

Airlines said they are monitoring the situation and recommending passengers allow enough time to get through screening.

A coalition of nearly three dozen trade groups and unions representing pilots, flight attendants, airports, travel associations and airlines warned that the shutdown’s impact could become more pronounced over time.

Air-traffic controllers are also working without pay. The Federal Aviation Administration is trying to recall some airline-safety inspectors and other technical employees who have been furloughed.

“This partial shutdown has already inflicted real damage to our nation’s aviation system and the impacts will only worsen over time,” the groups wrote to President Trump and congressional leaders in a letter seeking to end the shutdown last week.

TSA Administrator David Pekoske has approved a $500 bonus for uniformed screening officers, to be paid in the coming days in an effort to ease financial hardships and provide some reward for their work.

The Gazette’s Wayne Heilman and 9News contributed to this report.