Travelers complaining of hours-long security lines at LaGuardia Airport in New York City over the weekend are blaming short-staffing and the government shutdown for their long waits.

On Sunday, at least one Twitter user described the airport as a "mad house," and several users posted photos showing lines stretching much longer than is normal for the airport.

A representative for the Transportation Security Administration said the agency screened 2.22 million passengers on Sunday, calling it "a historically busy day due to holiday travel."

"TSA at LGA has the staff it needs to screen passengers to date, but wait times were affected," the person said. The standard screening wait has a maximum of 52 minutes, he continued, but photos posted by passengers appeared to show a different story.

News that airports may be understaffed because of agents calling out sick instead of working without pay was first reported by CNN on Friday. Hydrick Thomas, the president of the TSA employee union, told the network that call-out rates had increased by up to 300%, with some 170 agents calling out sick at New York's John F. Kennedy Airport last week.

Read more: TSA airport screeners have been working without pay during the shutdown and now many don't have money to get to work

In the CNN report, a TSA representative did not deny the callouts but said wait times had remained well within usual standards. Tyler Houlton, a press secretary for the Department of Homeland Security, which runs the TSA, called the report "fake news" on Twitter.

That irked Jeremy Villano, a Twitter user who asked whether the lines usually hit the airport's front door. "You need to stop lying," he said in response.

"This problem of callouts is really going to explode over the next week or two when employees miss their first paycheck," a union official at Dallas-Fort Worth International Airport told CNN. "TSA officers are telling the union they will find another way to make money. That means calling out to work other jobs."

On Monday, the government shutdown entered its 17th day, making it one of the longest in American history.