I have 3 AMEX credit cards (JetBlue, Blue, and SPG) and 1 charge (PRG). Oldest is JetBlue from 2005 and I got the PRG in December 2012. I've had the SPG card for about 3.5 years and I just sent a request for a CLI. I got the typical "we'll let you know in 7 days message." Today I received a letter in the mail saying the following:

Thank you for your recent request for a line of credit increase on your American Express Card Account.

We appreciate your interest and would like to process your application as son as possible. Before we can finish your application, we need to have you provide the following information.

It then asks for me to fill out an IRS 4506T form and at the bottom it says that if they don't hear from me within 30 days they will give no further consideration to my application.

Basically, is this an FR? If so, do I have to fill it out to keep myself in good standing with AMEX? I'd honestly rather not complete it even if it means I don't get my CLI, however, will this affect my status with AMEX in the future? I was planning on applying for a Platinum card in the near future. I wouldn't want this to affect my application for that, or the status of my existing accounts.