From the Federal Trade Commission’s Website:
If you decide that you don’t want to receive prescreened offers of credit and insurance, you have two choices: You can opt out of receiving them for five years or opt out of receiving them permanently.
To opt out for five years: Call toll-free 1-888-5-OPT-OUT (1-888-567-8688) or visit http://www.optoutprescreen.com. The phone number and website are operated by the major consumer reporting companies.
To opt out permanently: You may begin the permanent Opt-Out process online at http://www.optoutprescreeen.com. To complete your request, you must return the signed Permanent Opt-Out Election form, which will be provided after you initiate your online request.
When you call or visit the website, you’ll be asked to provide certain personal information, including your home telephone number, name, Social Security number, and date of birth. The information you provide is confidential and will be used only to process your request to opt out.
If you don’t have access to the Internet, you may send a written request to permanently opt out to each of the major consumer reporting companies. Make sure your request includes your home telephone number, name, Social Security number, and date of birth.