Travellers have been having a hard time getting through airports' security lines in the United States. But to make matters worse, they are now going to even have a harder time getting through long lines at the airport during Memorial Day.

The previous year on 2015, 2.25 million passengers underwent airport screening, as reported in CNN Money. This year, the number of passengers to travel and undergo airport screening, is predicted to increase this summer.

John Helmich, the chief economist in Airlines for America, an industry trade group, explained his prediction of how the airport security process would be for travellers. He said:

"If we're having long wait times processing early spring demand, then we expect late spring/early summer to be even worse."

Just previously this month, two airports in Chicago encouraged passengers to be at the airport at the minimum of three hours before their flight departs during the summer to be able to pass the TSA security screening.

Heimlich has admitted that he has been concerned, though, these long lines would become more frequent in the coming days. 222 million passengers got through airport security screening in June, July and August the previous year. This figures were an increase as compared to the data released in 2014, according to the trade group as reported by CNN Money as well. According to the same website, this year the figure can increase as much as 231 million passengers travelling in airports going through TSA screening.

At the Atlanta's airport, for instance, the line at the TSA security earlier this month was so long that it wound up at the airport's atrium before it got all the way through the domestic airport terminal area baggage claim section, as reported by The Atlanta Journal-Constitution, via USA Today. Atlanta's airport has been considered as the world's busiest airport, as written in a USA Today article.