(NEXSTAR) — In just a few days, the long-awaited enforcement of REAL IDs will begin. If you have an upcoming flight in the U.S. and don’t have a REAL ID-compliant ID, you may find yourself grounded.

Enforcement of the REAL ID requirement, which stems back to legislation passed following the 9/11 terrorist attacks, officially begins on Wednesday, May 7. While many Americans are already in compliance, having a driver’s license or state ID card sporting a star in the corner, DMVs throughout the country have reported long lines of those trying to get theirs.

REAL IDs are optional, and are generally only required if you’re flying within the U.S. or have to enter specific federal facilities. That does not include polling places, Social Security offices, hospitals, courthouses, or post offices, for example.

While optional, those flying without a REAL ID could “face delays, additional screening, and the possibility of not being allowed into the security checkpoint,” the TSA has warned. You are not exempt if you have TSA PreCheck, either.

Even without a REAL ID, you may still have a compliant means of identification that TSA will accept.

For example, if you live in the handful of states that issue an enhanced driver’s license or ID, you’re in compliance. A U.S. passport or passport card will also be accepted (a REAL ID does not double as a passport; international travelers will still require a passport, plus any additional visas or travel documents).

Other alternate forms of identification listed by the TSA, as of May 1, include:

• Foreign government-issued passport
• Veteran Health Identification Card
• DHS trusted traveler cards
• Department of Defense ID (including those issued to dependents)
• Permanent resident card
• Border crossing card
• Acceptable photo ID issued by a federally recognized Tribal Nation/Indian Tribe, including Enhanced Tribal Cards
• HSPD-12 PIV cards
• Canadian provincial driver’s license or Indian and Northern Affairs Canada card
• Transportation worker identification credential
• U.S. Citizenship and Immigration Services Employment Authorization Card (I-766)
• U.S. Merchant Mariner Credential

The TSA has warned, however, that the aforementioned list of acceptable IDs “is subject to change without notice. TSA strongly encourages you check this list again before traveling, so you do not arrive at the airport without acceptable ID.”

If you do not have a REAL ID or any of the accepted IDs listed above, the TSA says you may be asked by one of its officers to “complete an identity verification process.” During this process, identifying information about you, like your name and address, will be collected to confirm your identity.

Once confirmed, you will be allowed into the security checkpoint but “may be subject to additional screening.”

“You will not be allowed to enter the security checkpoint if you choose to not provide acceptable identification, you decline to cooperate with the identity verification process, or your identity cannot be confirmed,” the TSA says.

If you still need a REAL ID, getting one should be relatively easy, despite the potentially long lines at your DMV. At minimum, you’ll need to provide documentation that shows your full legal name, your date of birth, your Social Security number, two proofs of address for your principal residence, and your lawful status.

Four documents — your birth certificate and your Social Security card (or, in some cases, just the number), plus a bill and a pay stub — could help you meet all of those requirements. You may, however, need different or additional documents depending on your situation.

Ultimately, you’ll want to check with your local DMV to determine qualifying documents and roughly how long it will take for your REAL ID to be available. If you have additional questions about REAL IDs, you can visit TSA’s website, DHS’s website, or contact your local DMV.

It’s worth noting that children under the age of 18 do not need to provide identification while flying within the U.S.