Type your authorization letter. Do not handwrite it. If the passport agents at the Department of State cannot decipher your handwriting, they cannot release the passport to anyone but you.
Refer to your specific travel company's website to see if they have posted any sample authorization letters stating the specific rights they will need to obtain your passport once the paperwork is finished (see Resources).
Specify the travel agency's name within the letter, granting them and all their representatives the sole right to have access to your passport. Authority letters stating travel agencies in general form will not be accepted.
Include a clause in the letter that will grant the passport agency's representatives the right to discuss matters pertaining to the processing of your passport application, such as your personal information or proof of citizenship. By doing this, you will allow the representative to handle small issues or questions the Department of State may have about your application without slowing the process down.
Date the letter!
Ask your travel agency if they need you to sign the letter in their presence. Sometimes, the travel agency will have a public notary on site who will notarize the letters for added security. Sign your name on the letters the exact same way you have written it on your passport application.
Provide as many signed copies to the passport agency as it requires. Do not submit photocopies in lieu of a signed original. Photocopies will not be accepted.