Flight delays started to climb Tuesday evening across the United States amid air traffic controller staffing challenges, as people responsible for guiding planes through the skies approach nearly a week of working without a paycheck.

According to FAA airport data, flights are being delayed this evening at Nashville International Airport due to “staffing,” with average arrival delays of 126 minutes as of 5:30 p.m. Eastern. Staffing is also responsible for active or expected delays at Chicago O’Hare International Airport, Dallas Fort Worth International Airport and at airports in Teterboro and Newark, New Jersey, both reliever airports for the busy New York City airspace.

The National Air Traffic Controllers Association union didn’t immediately respond to a request for comment. The Federal Aviation Administration didn’t either, but in an automatic email reply said that due to the lapse in congressional funding it is not responding to routine media inquiries.

It’s the second day in a row that staffing issues have forced flight delays, though on Monday they were at Hollywood Burbank Airport near Los Angeles. That shortfall was isolated and late enough in the evening that the disruption was not wide-reaching. But if airport controller absences continue, especially earlier in the day, flight delays will stack up geometrically and could exert enormous political pressure on lawmakers to end the shutdown.

The Transportation Department earlier this week warned that it had noticed an uptick in controllers calling out sick, though the agency hasn’t explicitly connected that phenomenon to the delays seen Tuesday evening.

But it wouldn’t be the first time some air traffic controllers got tired of a government shutdown and opted to stay home. During the last prolonged shutdown in 2019, which lasted 35 days, controllers were widely credited with having brought it to an end by calling out sick, which in turn forced delays across the country.

When a facility doesn’t have enough capacity to handle flights, the FAA will slow traffic, which causes delays to spike.

Controllers are set to receive a partial paycheck Oct. 14, and the first “fully missed” one is slated for Oct. 28, according to DOT.

Political sniping over the issue was in high gear on Tuesday as Transportation Secretary Sean Duffy tussled with Democratic Gov. Gavin Newsom of California over social media regarding the Burbank airport delays.

In one X post early Tuesday, for example, Duffy said: “.@CAGovernor you are unbelievable. The reason we are shut down is because YOUR party can’t get its priorities straight. Democrats prioritize things like free healthcare to illegal immigrants over making sure our hard-working air traffic controllers at Burbank airport get paid.” Newsom’s press office responded, saying Duffy was “whining” on television.

House Minority Leader Hakeem Jeffries (D-N.Y.), meanwhile, in a statement provided to POLITICO said the claim that Democrats are responsible for travel delays and staffing issues is “laughable.”

“Secretary Duffy should ask his boss in the White House to call off his out-of-control OMB Director who is threatening to illegally fire civil servants instead of making performative appearances on cable TV designed to scare federal workers,” Jeffries said.

DOT didn’t immediately respond to a request for comment about Jeffries’ statement.