The US government is to start charging UK travellers $14 (£9) to apply for permission to enter the country.
The compulsory Electronic System for Travel Authorisation (Esta) is free at present, but from 9 September visitors to the US will have to pay for it.
It lasts for two years; people who already have a valid form will not have to pay until their current one expires.
The scheme was introduced in January 2009 but was made mandatory from January 2010.
It applies to all 35 countries with US "visa waiver" status.
The Electronic System for Travel Authorisation form, which takes up to 72 hours to be approved, gives air passengers prior approval for entry to the US.
It replaced the green I-94 card which passengers have previously filled in on their flight into the US.
End Quote Martin Lewis MoneySavingExpert.com
Most people who fill in the form should receive approval from the US Department of Homeland Security within a few minutes.
But British Airways and American Airlines are advising travellers to apply at least 72 hours in advance.
Both airlines have said people without valid Esta forms or visas will not be allowed to board flights to the US.
The fee has been introduced to fund a programme which aims to promote tourism in the US and attract foreign spending.
Martin Lewis, creator of MoneySavingExpert.com, has urged people even considering a trip to the US to apply for a form now to beat the charge.
He said: "The security authorisation lasts for two years, so do it now and it'll be free if you travel in that time. Yet leave it for a month and you'll have to pay for it.
The US Senate has passed the Travel Promotion Act to set up a non-profit Corporation for Travel Promotion.
US President, Barak Obama, is set to sign the act this week, meaning it will become law within ten days.
Under the act, travellers from countries that do not require a visa to enter the US, including the UK, will have to pay to complete the Electronic System for Travel Authorisation (ESTA) before travelling.
The charge will be at least $10, but could be as much as $17 per person.
The authorisation will be valid for two years, or for the length of the applicant's passport, whichever is sooner.
After that, each visitor will need to repay the fee.
The money will go into a Travel Promotion Fund. A further $100m will come from private sector contributions.
Roger Dow, president and chief executive of the US Travel Association, said the new body could become the largest national tourism communications programme in the world.
He described the move as ‘an historic victory for the US economy’.
Currently the ESTA is free.
Full story and background via e-tid