A business letter of responsibility is required, to be typewritten on your company letterhead and addressed to:
Consulate General of Vietnam, Visa Section, Houston, TX
The letter must explain all of the following:
Nature of business to be performed
Name and address of reference to be visited
This letter should request Multiple Entries visa if required
Guarantee of return transportation and sufficient funds for the visit
The letter should be signed by an officer of the company other than the applicant.