• Americans will soon need to apply for a travel authorization to visit 30 countries in Europe.
• The application has a nonrefundable fee of 7 euros a person, or about $7.40.
• Travelers must get the authorization via the European Travel Information and Authorisation System prior to their trip. It's expected to be operational sometime in 2024.
• The new system is meant as a security measure.

Americans will soon have to apply for a travel authorization to visit Europe, and failing to get one may ruin your next trip.

The requirement, slated to start in 2024, currently applies to 30 European nations, including popular destinations such as France, Germany, Greece, Italy, Portugal and Spain.

Travelers must apply for the travel authorization via the European Travel Information and Authorisation System, or ETIAS, prior to their trip.

The online application carries a nonrefundable fee of 7 euros a person, or $7.40 at prevailing exchange rates as of noon ET on Thursday. People under 18 years old or over 70 years old are exempt from payment.

More from Personal Finance:
Passport delays are still long: Apply at least 6 months ahead of travel
How you can save $500 or more on a flight to Europe this year
A controversial hack to save on plane tickets carries a 'super big risk'

Europe is the top destination region for international travelers from the U.S., according to travel app Hopper. But Americans won't be allowed to visit without the authorization.

"If you forget to do it, you won't board the plane," said Sofia Markovich, a travel advisor and founder of Sofia's Travel.

Why Europe is requiring a travel authorization

The authorization isn't a visa and doesn't guarantee entry. Travelers with a valid visa don't need the authorization.

In 2016, the European Commission proposed to establish the ETIAS to strengthen security checks on Americans and nationals from roughly 60 other nations who are able to visit Europe's Schengen area without a visa.  

The new European system is similar to one the U.S. put in place in 2008.

"After 9/11, things changed in the world," Markovich said. "It's really about keeping things safe and knowing who comes in and who goes out."

When travelers should apply

The good news: Travelers don't have to do anything yet.

The European Union expects the ETIAS to be operational in 2024 but hasn't set a firm rollout date. The program isn't yet accepting applications.

"There is nothing anyone can do or needs to do now," Sally French, a travel expert at NerdWallet, said. "But it's something they need to keep tabs on."

The requirement has already been delayed a few times and could be again, French said. It was initially meant to take effect in 2021 and then in 2023.

Most applications will be processed in minutes and within 96 hours at the latest, according to the EU. However, it can take up to an additional 30 days for travelers asked to provide extra information or documentation or do an interview with national authorities, the EU said.

"As soon as you make the booking, make sure you file for your ETIAS," Markovich said.

The EU even strongly advises obtaining the travel authorization before buying tickets and booking hotels.

"Seven euros is small potatoes in the scheme or your European trip," French said of the application fee. "You don't want to have paid for the flights, hotels and tours, and realize you can't take the trip because of this small step."

The ETIAS authorization is valid for three years or until your passport expires, whichever comes first. Travelers with a valid ETIAS don't need to apply for a new one each time they visit Europe.

Don't miss these CNBC PRO stories:

• This bank just hiked its 1-year CD rate to a fresh high
• A low-cost way to protect against an S&P 500 drawdown as risks escalate
• How to invest $1 million for the next decade, according to private bankers and wealth advisors
• This highly profitable industry is booming as the population ages
• Bank of America sees risks for employers as insurance coverage of weight loss drugs grows