I would wait to see the letter. It seems unlikely that American Express would even accept copies you made yourself. See this thread (beginning at post 217) for discussion of difference between IRS forms 4506T and 4506:
I received the letter from AX today. It states:
"In order to complete the processing of your application, we need the following information:
Complete copies of your past 2 years signed personal tax returns.
Complete copies of your past 2 years business tax returns."
So should I call them and ask about the form 4506? I will NOT send copies of these returns through the mail. The information is too sensitive and there would be over 200 pages of documents I would send. What should I do?