Today I asked one of Thailand customer if they need invitation letter for visiting us.

He replied that they have the APEC Card and don't need the invitation letter.

What is APEC Business Travel Card, I am curious.

Most APEC economies are full participating economies in the APEC Business Travel Card: Australia, Brunei Darussalam, Chile, China, Hong Kong, Indonesia, Japan, South Korea, Malaysia, Mexico, New Zealand, Papua New Guinea, Peru, the Philippines, Singapore, Taiwan, Thailand and Vietnam.^[1] Russia began full participation on 1 June 2013.^[2][3]

Citizens of these economies can apply for a Card at their national government, upon which moment their names are circulated amongst the other participating economies which give entry pre-clearance when all conditions are met. After this moment, the card can be used for visa-free entry.

Two economies are transitional members: United States and Canada. This permits them to issue APEC cards to their own citizens and nationals (who can benefit from visa-free travel to other APEC members) without having to grant visa-free travel status to citizens and nationals of other APEC members (though they may benefit from expedited border crossings and/or visa appointments from the United States and Canada).^[4] However, as of Sep 2013, neither the United States nor Canada has begun issuing the APEC cards, though domestic legislation permitting the program has passed in the United States.^[5]

It is also possible for a citizen of a third party country (including the United States and Canada) who is also permanent resident of Hong Kong to apply via Hong Kong immigration; for example a British citizen who is a permanent resident of Hong Kong can apply via the Hong Kong Immigration Department for an APEC card. This exception does not apply to any other member countries