visa passport
© Jonathan Ernst / Reuters
They were previously allowed to use mere driving licenses.

But residents of some US states may soon require additional ID, such as passports, if they wish to embark on air travel - even if just domestically.

That's the new procedure on the horizon for people from states that have not yet introduced the standards required by the 2005 Real ID Act, which demands stricter regulations for state-issued IDs.

The states that haven't yet fallen into line each now have a grace period of three months to meet the revised criteria.

This deadline expires on 22 January 2018.

Travellers with drivers licenses from states that miss the deadline won't be able to use them as ID - for international or domestic flights - and will risk being detained at airport security if they don't have a passport or other TSA-approved form of identification, such as a green card, border crossing card or military ID.

At the time of writing, according to the Department of Homeland Security's website, only 27 US states are compliant with the Real ID Act.

Many are listed as being under review.

The legislation, which was established after the 9/11 terrorist attacks, makes it harder to obtain a driver's license with counterfeit records.

US congress passed the act 10 years ago, but it wasn't enforced until 2013.

By October 2020 the entire country will need to meet the revised standards, or face strict travel limitations.

The US Department of State recommends allowing up to six weeks for passports to be completed and returned, although people can pay for a faster turn-around of 21 days.