Why You Don’t Want to See These Four Letters on Your Boarding Pass

Navigating through airports can already be a lengthy process, but there’s one code you’ll want to keep an eye out for.

If you see the letters SSSS printed on your boarding pass, getting through the airport could become a much lengthier process.

The four letters stand for “Secondary Security Screening Selection” and mean that the Transport Security Administration (TSA) has selected you for an enhanced security screening.

Along with a full search, passengers in this situation can expect to get screened through portable metal detectors, in addition to potentially receiving a full-body pat-down inspection and having their carry-on baggage opened and examined.

Related: Everything You Need to Know About TSA Approved Carry-on Luggage

According to a TSA spokesperson, passengers who have the code on their boarding passes are selected through the TSA’s Security Flight System, a prescreening program that identifies both low and high-risk passengers before they get to the airport.

This system will match up names against trusted traveler lists and the TSA’s watchlist before taking the screening instructions back to the airlines and identifying whether passengers are low-risk and eligible for TSA Pre Check, are on the Selectee List for enhanced screening, or will simply receive the standard screening.

While cases like buying a last-minute one-way flight that is pricey or paying for a flight in cash could sometimes land you on this list, according to Skift, the TSA also said the selections can happen at random.

When a passenger has an SSSS on their boarding pass, they typically won’t be able to print it out online and will be told they’ll need to go to the airport to do so. If this is the case for you, you’ll want to give yourself at least 30 minutes of additional time to make sure you make your flight.

Additionally, if you’re interested in getting off of the list, you can apply for a Redress Number.

This article originally appeared on Travel + Leisure