Travelers across the United States will face new identification requirements at airports on Wednesday as the Transportation Security Administration begins enforcing the REAL ID mandate.

“If they do not have any acceptable ID, we strongly suggest they arrive to the airport 3 hours prior to their departure time,” Velez told Gizmodo. Even if you arrive early, however, there’s no guarantee you’ll be allowed to board your flight. So it’s much easier if you just have a Real ID that you can hand over to security.

Passengers who do not have a TSA-acceptable form of identification can experience delays, additional screening, and possibly be denied entry.