It's about to cost you a little more to visit the United Kingdom.

Starting today, Americans, Canadians, and many other foreign visitors will have to pay 10 British pounds ($12.34) for an electronic travel authorization (ETA) before traveling to the U.K. as part of a visa waiver program. "Everyone travelling needs to get an ETA, including babies and children," a U.K. government website said.  

European Union (EU) citizens will need an ETA starting April 2. There are just a handful of exceptions to the requirement, including if you're a British or Irish citizen, or already have a U.K. visa.

Visitors must apply for an ETA before traveling to the U.K. but are allowed to travel while awaiting a decision, which the government said will "usually" arrive within three working days.

The ETAs are good for two years, and you can visit the U.K. "as many times as you want during that time," according to the U.K. goverbment. However, "If you get a new passport, you will need to get a new ETA."

US Has Similar Requirement for Dozens of Countries

Foreign visitors to the U.S. from 42 countries participating in the Visa Waiver Program—including the UK—must pay $21 for "authorization through the Electronic System for Travel Authorization (ESTA) before beginning your trip," according to USA.gov.

It grants citizens of listed countries permission to travel to the U.S. for business or tourism for up to 90 days without a visa. Approved applications are valid for two years and allow multiple visits during that time.