Information needed to fill out an authorization letter includes identification of the parties involved, details about the authorization you are granting, and the reason for the authorization, according to Easy Pave Learning. It must also include dates for the authorization, any authorization restrictions, a signature and a witness.
The authorization letter should follow the standard format of a business letter, notes Easy Pace Learning. Write your name on the first line, your street information on the second line, and your city, state and ZIP code on the third line. All lines should be single spaced. Write out the full date without abbreviation. Write the recipient's information in the same format as your information, using his full name and title. You may have to leave this portion blank if you do not know the identifying information of the party.
Provide specific details about the authorization being granted, explains Easy Pace Learning. For example, for legal matters, include the case number. For letters regarding medical information, include your medical insurance number and claim information. For financial matters, include applicable account information. Explain your need for a representative. Your witness must observe you signing the authorization letter to ensure that you are the person giving the authorization by your own will.