Hundreds of Transportation Security Administration agents have called out of work at major airports across the US, causing travel misery for thousands of frustrated passengers.

Staffers are calling in sick in huge numbers because they don't want to work for free during the government shutdown, which is now in its third week.

It meant huge lines of frustrated travelers formed at major hubs including New York's LaGuardia and John F. Kennedy International Airports, Dallas-Fort Worth, Charlotte, Salt Lake City, Minneapolis Saint-Paul and Bradley International in Connecticut.

Wait times were around 90 minutes at the Delta Airlines terminal at the LaGuardia Airport on Sunday and TSA Precheck, which usually expedites travel security, was completely closed.

TSA agents are among the 420,000 federal employees who are contractually required to work amid the shutdown without pay, so they have chosen to use their sick days instead.

Other employees at other agencies were furloughed and are at home without a paycheck.

More than 51,000 of the agency's staffers are involved in the airport screening process which is essentially for people to travel across the United States.

Some travelers posted on social media that they asked TSA agents if they could tip them as they weren't getting a wage, while others offered to donate food.

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Hundreds of TSA agents have called out of work within the last week at major airports across the US, causing travel misery for thousands of frustrated passengers. Frustrated passengers are seen waiting in line at the Delta Airlines terminal at LaGuardia Airport on Sunday

TSA employees tried to calm passengers down as they worked to get them through security

Wait times were around 90 minutes and TSA Precheck, which usually expedites travel security, was also closed at that checkpoint

As many as 170 TSA agents have called out each day within the past week at JFK.

According to CNN, TSA employees at JFK, who worked a morning shift, were required to work extra hours to cover the gaps.

At the Dallas-Fort Worth airport, call outs have increased by 200%-300%, according to the news outlet.

During an average shift, the airport can expect between 25 to 30 TSA employee call outs.

The staffing shortages have also hit the Charlotte and Raleigh-Durham airports in North Carolina.

Those two airports reported TSA call outs being 10 per cent higher than usual.

On Sunday, passengers also reported long lines at the Seattle–Tacoma International Airport, Utah's Salt Lake City airport and the Bradley International Airport in Connecticut.

According to Sarah Burgisser, who works for one of the airlines at Sea-Tac, several passengers missed their flights over the weekend.

Burgisser told KIRO 7 that during her Saturday shift, 'a lot, a lot of passengers' missed their flights.

'I really feel sorry. We had to close the flight to be on time. Because - we give them a couple of minutes, but we can’t wait forever,' she added.

It's unclear how many travelers missed their flights over the weekend.

A passenger at the Spokane International Airport in Washington state said there were 'extra long lines', but said that TSA workers were 'still working hard with a smile despite the fact they aren’t getting a paycheck'.

Some passengers at the Minneapolis–Saint Paul International Airport shared photos of snaking lines as they waited to get through security.

On Sunday, passengers reported long lines at the Seattle–Tacoma International Airport, Utah's Salt Lake City airport (pictured) and the Bradley International Airport in Connecticut

Some passengers at the Minneapolis–Saint Paul International Airport shared photos of snaking lines as they waited to get through security

'This is the TSA screening line for Terminal 2 at MSP this morning. It extends out to the parking garage. MSP officials are missing in action. Thanks Trump,' a Twitter user wrote.

One Twitter user joked that she 'asked TSA agent if I should take out my laptop out of its case and she said "I don’t care, I’m not getting paid."'

The passenger said she was flying out of the Minneapolis-Saint Paul airport when she made the joke on Twitter.

A TSA employee told the Gothamist that 'it's hard, because people have bills to pay'.

'If you got spouses, family, friends that can help you stay aboard until you get your pay, it’s really not too harsh. But everybody is not in that same boat,' the officer said.

The agent said he's had to call his creditors to see if he can defer payments on his rent, car and utility bills.

The TSA is one of the lowest-paying federal agencies with a typical starting salary of about $17,000 per year.

Hydrick Thomas, a union rep for the American Federation of Government Employees, which represents TSA workers across the country, told Gathamist: 'You lose a day’s pay, it can have a total effect on how you manage your livelihood.'

While this could be perceived as a form of protest, union officials believe it’s more likely that TSA employees are working at their second jobs to pay their bills.

'This is the TSA screening line for Terminal 2 at MSP this morning. It extends out to the parking garage. MSP officials are missing in action. Thanks Trump,' a Twitter user wrote

One Twitter user joked that she 'asked TSA agent if I should take out my laptop out of its case and she said "I don’t care, I’m not getting paid"'

A passenger shared this photo of 'extra long lines' Monday morning at the Spokane International Airport in Washington State

TSA lines in Orlando (pictured) were also significantly longer as one passenger hoped to make his flight

Lines were also long at the Oakland International Airport (pictured) in California

Hours after the CNN report was published, the Department of Homeland Security (DHS) denied that there were mass call-outs, insisting 'security effectiveness will not be compromised and performance standards will not change'.

A DHS spokesperson lashed out on a personal Twitter account, following an earlier report the non-payment of some 800,000 government employees could harshly effect travelers during the tough period due to the TSA being affected.

Alleging 'fake news' had 'grossly misrepresented' the figures related to the air travel industry, Tyler Q. Houlton denied that it was creating a vulnerability and less workers strive to do more than usual.

He posted online: 'Security operations at airports have not been impacted by a non-existent sick out.'

NPR reporter Neda Ulaby tweeted that a TSA agent burst into tears when she offered them a tip

Many on social media urged their fellow passengers to show sympathy for TSA agents

Others offered to donate unopened snacks to agents they might have to throw away

Another Twitter user slammed the 'ridiculous' shutdown after one TSA agent joked that they were accepting donations of canned food

His angry response was followed by an official statement from the TSA which admitted more workers than usual were quoting illness when taking days off, but appeared to put it down the holiday season.

'Call outs began over the Holiday period and have increased, but are causing minimal impact given there are 51,739 employees supporting the screening process,' the tweet said.

On Monday morning, TSA released a statement that said the agency screened 'approximately 2.22 million passengers' nationwide on Sunday.

'99.8% of passengers waited less than 30 minutes; 90.1% of passengers less than 15 minutes,' the statement read.

Passengers in the agency's Pre-Check lines 'on average waited less than five minutes'.

'We are grateful to the more than 51,000 agents across the country who remain focused on the mission and are respectful to the traveling public as they continue the important work necessary to secure the nation's transportation systems.'

Sunday's delays come during the third week of the government shutdown that has left nearly 800,000 federal employees without pay and barely a week after the largest pilot union in the world urged President Donald Trump to put an end to the government shutdown.

The Air Line Pilots Association, which represents more than 61,000 pilots from 35 US and Canadian airlines, wrote a letter to the president warning that the continuing impasse was threatening 'the safety, security, and efficiency of our national airspace system'.

'The nation’s airspace system is a complex transportation network that involves government and industry partnerships to function properly, and the disruptions being caused by the shutdown are threatening the safe operations of this network,' according to the letter written by Captain Joe DePete, the president of the union.

'The government agency partners in the Department of Transportation (DOT) and Department of Homeland Security (DHS) have dual roles.

'They are both regulators and service providers.

'When any of their responsibilities are placed on pause due to a shutdown there are safety, security and efficiency gaps that immediately emerge,' the letter read.

Pilot union pens powerful letter to Trump demanding he put an end to the government shutdown Last week, the Air Line Pilots Association, urged the president to end the government shutdown that is now going on three weeks. The association, which represents more than 61,000 pilots from 35 US and Canadian airlines, warned Trump that the shutdown threatens ‘the safety, security, and efficiency of our national airspace system'. The shutdown is affecting the Federal Aviation Administration, which employs air traffic controllers, maintenance personnel, and airline security staff. During the shutdown, they are being forced to work without pay. In the letter, Captain Joe DePete, the President of the association, writes that working without pay places undue stress on these employees. The Air Line Pilots Association wrote a letter to President Trump warning that the continuing impasse was threatening ‘the safety, security, and efficiency of our national airspace system' The letter was also carbon copied to the top Congressional leadership - House Speaker Nancy Pelosi and Senate Minority Leader Chuck Schumer; and Senate Majority Leader Mitch McConnell and House Minority Leader Kevin McCarthy of the Republicans Advertisement

But despite calls for the shutdown to end, Trump has continued to stand by his demands for funding for a border wall as another round of shutdown talks failed to break an impasse.

The president, who spent part of the day at Camp David for staff meetings on Sunday, showed no signs of budging on his demand of more than $5billion for a wall along the US-Mexico border.

White House officials affirmed that request in a letter to Capitol Hill after a meeting with senior congressional aides led by Vice President Mike Pence at the White House complex yielded little progress.

The letter from Office of Management and Budget Acting Director Russell Vought also formalized Trump's declaration that the wall would be built from steel, rather than concrete, asking for funding for a 'steel barrier on the Southwest border'.

The White House said the letter, as well as details provided during the meeting, sought to answer Democrats' questions about the funding request.

Democrats, though, said the administration failed in both the meeting and the letter to provide a full budget of how it would spend the billions requested on the wall, money the president wants from Congress.

Sunday's delays (passengers waiting in line) come during the third week of the government shutdown that has left nearly 800,000 federal employees without pay

The letter includes a request for $800million for 'urgent humanitarian needs,' a reflection of the growing anxiety over migrants traveling to the border - which the White House said Democrats raised in the meetings.

And it repeats some existing funding requests for detention beds and security officers, which have already been panned by Congress and would likely find resistance among House Democrats.

Still, the request makes clear a wall is a top priority. Vought writes that a 'physical barrier - wall - creates an enduring capability that helps field personnel stop, slow down and/or contain illegal entries'.

Trump sought to frame a steel barrier as progress as he returned from the presidential retreat in Maryland, saying Democrats 'don't like concrete, so we'll give them steel'.

The president has already suggested his definition of the wall is flexible, but Democrats have made clear they see a wall as immoral and ineffective and prefer other types of border security funded at already agreed upon levels.

With the partial shutdown in its third week, House Speaker Nancy Pelosi said she intends to begin passing individual bills to reopen agencies in the coming days, starting with the Treasury Department to ensure people receive their tax refunds.

That effort is designed to squeeze Senate Republicans, some of whom are growing increasingly anxious about the extended shutdown.

The seemingly intractable budget showdown marks the first clash for Trump and Democrats, who now control the House.

It pits Trump's unpredictable negotiating stylings against a largely united Democratic front, as many Republicans watch nervously from the sidelines and hundreds of thousands of federal workers go without pay.

Although Trump tweeted that the Sunday session had been 'productive,' two Democrats familiar with the meeting gave a different take, saying the White House had not provided the budget details they had requested and again declined to re-open government.

One of the officials - neither was authorized to speak publicly - said no additional meetings were scheduled.

Trump said earlier in the day that he was hoping for 'some very serious talks come Monday, Tuesday, Wednesday'.

On Sunday, Trump stood by his demands for funding for a border wall as another round of shutdown talks failed to break an impasse. The president showed no signs of budging on his demand of more than $5billion for a wall along the US-Mexico border

While insisting he wanted to make a deal, he also declared he would not give an inch in his fight for funding for a border barrier, saying: 'There's not going to be any bend right here.'

Among the Republicans expressing concerns was Sen Susan Collins, R-Maine, who said Senate Majority Leader Mitch McConnell should take up bills from the Democratic-led House.

'Let's get those reopened while the negotiations continue,' Collins said on NBC's Meet the Press.

Democrats criticized McConnell for waiting on Trump's support, but Collins said she was sympathetic to McConnell's opposition to moving legislation without agreement from the president.

Several Republicans pushed the Interior Department to find money to restaff national parks amid growing concerns over upkeep and public safety.

And Senate Minority Leader Chuck Schumer, D-NY, suggested Sunday that pressure would only mount amid the shutdown, which he said is disrupting Transportation Security Administration operations, home loans and farmers in his state.

'Democrats and now a growing number of Republicans are coming together and saying let's open up the government and debate border security separately,' Schumer told reporters in New York.

Adding to concerns, federal workers might miss this week's paychecks.

Acting chief of staff Mick Mulvaney said on NBC's Meet the Press that if the shutdown continues into Tuesday, 'then payroll will not go out as originally planned on Friday night'.

Trump reaffirmed that he would consider declaring a national emergency to circumvent Congress and spend money as he saw fit.

The president also asserted that he could relate to the plight of the hundreds of thousands of federal workers who aren't getting paid, though he acknowledged they will have to 'make adjustments' to deal with the shutdown shortfall.

Trump also tweeted that he didn't care that 'most of the workers not getting paid are Democrats'.

The president said he planned to call the heads of American steel companies in hopes of coming up with a new design for the barrier he contends must be built along the southern border.

His administration has already spent millions constructing wall prototypes near the border in San Diego.