Flight passengers are warned things could get worse amid DHS shutdown, delays and callouts

As American airports and travelers continue to suffer the impacts of the DHS shutdown - and as TSA officers continue to go without paychecks - some European countries are warning those who would potentially visit the U.S.

It goes on, "Check with your travel provider, departure airport or airline for the latest guidance."

The delays are occurring because Transportation Security Administration (TSA) officers are calling out from work after going unpaid for the third time in nearly six months.

There was a national callout rate of 10.19% on Sunday, a TSA spokesperson told Fox News Digital this week.

That's the highest rate the agency has seen.

On Tuesday, the Hartsfield-Jackson airport in Atlanta cautioned travelers about delays in an X-post - and called out passengers for attempting to hack the system.

"We are seeing increased congestion at the International Terminal Checkpoint caused by domestic travelers attempting to bypass lines in the Domestic Terminal," wrote airport officials. 

"If you are flying domestically, please use the Domestic Security Checkpoints. At this time, wait times at the International Checkpoint are longer than those at the Domestic Terminal."

Callout rates have spiked nationwide, with the highest single-day airport callout rate reaching 55% at Houston Hobby Airport on Friday.

It takes four to six months to train and certify officers - creating a critical staffing gap, Fox News Digital was told by a source familiar. 

Travel expert Clint Henderson of The Points Guy website told Fox News Digital that as the shutdown drags on, flight passengers can expect the situation to only get worse. 

"TSA workers are going without pay, and some are quitting. Others are having to pick up gig work to pay the bills," said Henderson. 

"Mornings seem to be the worst times. Be sure to keep an eye on local news sites and social media in case of long lines. Some airports update wait times on their homepages, though - so keep an eye on that." 

Flight passengers have the right to request a prompt refund if the airline cancels the flight, said Henderson, or if it is severely delayed and the passenger decides not to accept the alternative bookings. 

"You are entitled to a prompt refund of your original payment method within 21 days," he said.