With screeners already calling in sick in larger-than-normal numbers, U.S. airports are girding for disruptions next week if the partial government shutdown continues and Transportation Security Administration officers miss their first paycheck.

The airport security officers are caught in the political fight in Washington between President Donald Trump and congressional Democrats over money for a wall along the Mexican border. Thirteen federal departments and agencies have largely closed down operations since Dec. 22 because funding hasn’t been approved.

The 51,739 TSA officers, who screen bags and passengers at U.S. airports, are considered essential to security and were ordered to continue reporting for duty even though funding for their agency has been halted. In recent days the screeners have called in sick in growing numbers, according to the agency.

The sick calls have contributed to longer wait times at unspecified airports, but major disruptions haven’t been reported so far, said Christopher Bidwell, a senior vice president for security at the Airports Council International-North America in Washington.

“We’re concerned that a prolonged government shutdown could potentially impact security and wait times at airports,” Bidwell said.

Airports are conducting talks with local TSA managers about finding ways to bolster TSA staffing, he said. Non-TSA employees aren’t permitted to screen bags and people, but can help at checkpoints by returning bins and managing lines.

“It’s certainly not built into their budgets right now, but if it came down to it they may look to find the resources to support that sort of thing on a voluntary and temporary basis,” Bidwell said.

So far, TSA is managing the small increase in officers not reporting to work, agency spokesman Michael Bilello said. On Sunday, more than 2.2 million people were screened at U.S. airports and more than 90 percent waited less than 15 minutes, Bilello said.

Wait times were normal at most large airports, according to agency data. New York’s LaGuardia Airport had waits that extended to 52 minutes, but that was because of unexpected traveler volume and management decisions, not because of staff shortages, he said.

TSA is taking multiple steps to ensure it can continue to perform screening. The agency has activated what it calls its National Deployment Force, which allows officers to be shifted to different airports to make up for staff shortages, Bilello said.

“If we go past Friday without a paycheck, that will be the first missed paycheck. Now we’re talking about a completely different environment,” he said. Officers have been paid up until now and are scheduled to receive a check on Friday.

After previous government shutdowns, Congress has passed legislation paying workers who were furloughed or who worked without receiving salaries.

The new chairman of the House Homeland Security Committee, Representative Bennie Thompson, a Mississippi Democrat, wrote to TSA Administrator David Pekoske on Monday asking for more details about how workers are responding to the shutdown.

“I am concerned if wait times and public pressure increase, some TSA managers may try to manage the effects of the shutdown in ways that are detrimental to security,” Thompson said.

Airport screeners may still get their pay on time Friday if the impasse is resolved by midweek, Bilello said.

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