The ESTA, or Electronic System for Travel Authorisation, was introduced in January last year for a trial period but from 20 January it will be compulsory.
The ESTA, which is an online form, replaces the green card that was filled out by passenger onboard an American flight.
It is advisable for visitors to American to fill out the ESTA form at least 72 hours before departure. The ESTA takes about 15 minutes to complete, and although the vast majority of applicants will receive travel authorisation within minutes it can take up to 72 hours.
The new regulations to make the ESTA compulsory means that airlines will not be able to accept American-bound customers if they do not have ESTA approval, or a valid American Visa or Green Card.
The Travel Promotion Act, which proposes that America levy a US$20 stipend on the ESTA to fund travel awareness and passenger information, is currently in the Senate.