From Realtors. org. The article is here:
http://magazine.angieslist.com/Articles/2009/October/NATIONAL/appraisal-law.aspx
Keep in mind that it's an old article and this no longer applies exactly as written:
The old appraisal rules still apply for FHA-backed and other non-Fannie and Freddie loans. As a homeowner, you can still order your own appraisal to assess your home's value before testing the market.
