That small star adorning your U.S. driver’s license is about to help you avoid a $45 expense.

Starting this Sunday, travelers in the United States who lack a REAL ID or an alternative form of identification—such as a passport—will face a new fee when flying.

This isn’t a penalty or a fine. Instead, it covers the cost for travelers who haven’t complied with the REAL ID requirements to utilize the Transportation Security Administration’s new ConfirmID system for alternate identity verification. Be aware that this process demands additional time, and even after paying the fee, there’s no guarantee you’ll catch your flight.

The Department of Homeland Security reports that the majority of U.S. travelers have already met the compliance standards. The fee is designed to motivate the remaining travelers, those who still need a star-marked REAL ID, to obtain one.

For those who might be surprised by this new charge, here’s what you need to know:

What is a REAL ID?

A REAL ID is a federally compliant, state-issued license or identification card that fulfills heightened security requirements enacted following the September 11, 2001, terrorist attacks.

Obtaining the ID means taking more documents to the motor vehicle agency than most states require for regular IDs. It was supposed to be rolled out in 2008, but the implementation was repeatedly delayed.

The updated ID is indicated by a white star in a yellow circle in most U.S. states. It has been required since May, but travelers without it – and without another TSA-accepted ID – were still allowed through security with extra screening and a warning. That changes Sunday.

Who has to pay?

Travelers 18 and older flying domestically without proper identification on them will have to pay $45 to verify their identity at the airport through the ConfirmID process. If approved, the verification covers a 10-day travel period.

Paying the fee, however, does not guarantee access to U.S. air travel, and passengers whose identities cannot be verified may be turned away at airport security.

“This fee ensures that non-compliant travelers, not taxpayers, cover the cost of processing travelers without acceptable IDs,” said Adam Stahl, acting TSA deputy administrator.

How it works

The service fee is paid online at tsa.gov/ConfirmID. Travelers will have to enter their legal name and the start date of their travel. Accepted payment methods include debit and credit cards, Venmo and PayPal.

Someone other than the traveler can make the payment, according to TSA, but the traveler’s information must be entered correctly.

Passengers will then receive an emailed payment receipt from pay.gov.

At the airport checkpoint, show a government-issued ID and a digital or printed copy of the receipt to begin the verification process.

TSA recommends that travelers pay the fee before arriving at the airport to save on time, as the verification process alone could take up to 30 minutes.

Other accepted forms of ID

TSA accepts digital IDs through platforms such as Apple Wallet and Google Wallet at more than 250 airport checkpoints in the U.S.

The agency has a full list of acceptable IDs on its website. They include:

– Passport or passport card

– Permanent resident cards

– Trusted traveler cards, such as Global Entry or NEXUS

– Military IDs

– Photo IDs from federally recognized tribal nations