WASHINGTON (TNND) — The effects of the federal government shutdown continued to show up on airport monitors across the country on Wednesday as the Senate failed for a sixth time to pass a short-term budget.

The impasse leaves federal employees unpaid even as many of them are expected to continue working. The added stress is believed to be behind a recent increase in sick calls from air traffic controllers who are already in short supply and often work 10-hour days six days per week.

Between 2 p.m. and 6 p.m. On Wednesday, more than 500 flights out of U.S. airports were delayed. Boston Logan International Airport saw the highest rate, with half of all flights delayed during that window, according to FlightAware's "MiseryMap." Forty-one flights at Hartsfield-Jackson Atlanta International Airport were delayed, 36 at San Francisco International Airport, 34 at Chicago O'Hare International Airport and 33 at Dallas-Fort Worth International Airport.

LaGuardia Airport flights were temporarily halted due to a data outage, the Federal Aviation Administration said. Even before the outage, the airport experienced dozens of delays.

“When we’re put in a situation and as this continues on and people have to start making human choices of, do put food on the table? Do I take care of my kids? Am I a single parent?" said Nick Daniels, president of the National Air Traffic Controllers Association, a labor union representing more than 20,000 air traffic controllers, engineers and other aviation staff.

Next week, air traffic controllers will receive their last partial paycheck until the shutdown ends.

“Air traffic controllers are going to go to their primary job, but then they’ll start having to take up a second job to make sure they have a steady stream of income," Daniels said.

There's no evidence that the rise in sick calls is an organized effort or a form of protest against the lack of progress in Washington.

"Some of it is just part of normal you know, being out sick or dealing with a family situation. It happens all the time. The fact is that the Air Traffic Control facilities are short staffed so if you have one or two controllers you know, not showing up, calling in sick, that’s gonna affect that facility and the operation," Flight Safety Foundation CEO Dr. Hassan Shahidi said.

Working during the shutdown has been made more stressful by the fact that about 2,000 Air Traffic Control support staff have been furloughed.

Shahidi said he expects a "cascading effect" of delays heading into the weekend and next week as the FAA has a strict staffing threshold for each facility that cannot be breached.

"As we begin some of these threshold levels really being affected and the FAA has no choice but to delay. And a delay in Chicago, a delay in Washington, in New York and San Francisco, Los Angeles is going to have a nationwide effect," Shahidi said.

The nation has seen this before: Ground stops and mass delays along the east coast in early 2019 helped pressure Congress and President Donald Trump to end the longest-ever government shutdown of almost 35 days during which federal workers missed two paychecks.

“Air traffic controllers don’t start a shutdown and we don’t end a shutdown," Daniels said. "Politicians are the ones that start the shutdown and they’re the only ones that have the ability to end the shutdown.”