In fact, the Friday before is the fourth busiest day of the year for the industry, according to CNN Money. Airports saw 2.25 million passengers pass through TSA checkpoints on that day last year, and industry experts predict it will be higher this year.

This is a trend you’ll likely continue to see throughout the summer. As John Heimlich, chief economist for industry trade group Airlines For America, told CNN, Thursdays and Fridays during this season are generally some of the busiest days for airports. Last summer, between June and August, a record-breaking 222 million passengers went through airport security. That was a 4.4% increase from the year before, and it’s expected to go up this year by another 4%, to 231 million.

Airports have already been dealing with long wait times. “If we’re having long wait times processing early spring demand, then we expect late spring/early summer to be even worse,” Heimlich said. But it’s not just about the number of people traveling; it’s also about the people themselves. A lot of summer travelers don’t fly as often as those you may see at airports in the winter. That means they’re less familiar with TSA procedures, and can take longer going through checkpoints.

Heimlich warns that this congestion could have an effect on the industry: “If it starts being perceived as a chronic and structural problem, then certainly it could deter demand for air travel.”