Here's why some Americans might soon need a passport to fly within the U.S.

Frequent fliers who take international trips know to bring along their passport, but what about just for traveling around the country?

Beginning early next year, the REAL ID Act will tighten requirements to fly, and some states' driver's licenses might not make the cut.

Here's what you should know about the act.

What is REAL ID?

The REAL ID Act mandates what kinds of IDs can be used to access federal facilities, enter nuclear power plants and board federally regulated aircraft, in order to increase security in these areas. This means that, once the act goes into full effect, your state-issued ID must be compliant if you want to use it to board flights, including domestic.

How do I know if my state is affected?

Currently, a little more than half of states are compliant. If you live in one of these states, you can keep using your state-issued ID to fly. All other states are under review or have been given an extension. Residents of those states may have to use other forms of identification when the act goes into effect.

See which states are compliant and which are not yet.

Didn't this come up years ago?

The REAL ID legislation was passed by Congress in 2005. Since then, the Department of Homeland Security has been working with states to review state-issued IDs and decide which are REAL ID-compliant and what changes need to be made.

When does it take effect?

If you live in a non-compliant state, you can keep using your driver's license to fly domestically until the grace period ends on January 22, 2018. Some states have an extension and you can keep using it until October 1, 2020.

Editor's note: States that are currently "under review," such as California, may have plans to make REAL IDs available before the end of the relevant grace period or extension date.

Will I really need my passport to fly domestically?

If your state is not compliant by the end of its grace period or extension, you will need to fly with a different form of identification that is TSA-approved. You would need a passport unless you have a different form of accepted ID, such as a U.S. military ID. See the full list at the bottom of this factsheet.

If you are planning to fly using a passport and don't yet have one, start planning soon. Routine processing can take up to 6 weeks.

See the Transportation Security Administration's website for more FAQs about REAL ID.