Travelers to the United States from visa waiver countries must apply for electronic system travel authorization (ESTA) well before 72 hours else will be denied entry at US airports.
DHS issued a new announcement for travelers
REMINDER: Apply for ESTA no later than 72 hours before departing for the United States. Real-time approvals will no longer be available and arriving at the airport without a previously approved ESTA will likely result in being denied boarding.
Visa Waiver Program countries listed below
[1]With respect to all references to “country” or “countries” in this document, it should be noted that the Taiwan Relations Act of 1979, Pub. L. No. 96-8, Section 4(b)(1), provides that “[w]henever the laws of the United States refer or relate to foreign countries, nations, states, governments, or similar entities, such terms shall include and such laws shall apply with respect to Taiwan.” 22 U.S.C. § 3303(b)(1). Accordingly, all references to “country” or “countries” in the Visa Waiver Program authorizing legislation, Section 217 of the Immigration and Nationality Act, 8 U.S.C. 1187, are read to include Taiwan. This is consistent with the United States’ one-China policy, under which the United States has maintained unofficial relations with Taiwan since 1979.
The applications can be completed at the official DHS website here
