Did you receive a "Letter of Inquiry Concerning Michigan Taxes"? Was it dated September 10, 2010 and requires a response by October 26, 2010? If so, you are not alone.
It appears Michigan has sent out these letters to every out-of-state company with sales into Michigan (that it is aware of).
The letter requires companies to review their activities in Michigan and determine if they have nexus in Michigan. If you do, they give you the opportunity to fill out a Nexus Questionnaire and Voluntary Disclosure Request. If you do not have nexus, you still have to fill out the nexus questionnaire and explain why you don't have nexus.
The Voluntary Disclosure Request will require your company to file Michigan Single Business Tax (SBT) Returns or Michigan Business Tax (MBT) Returns for the 3 or 4 previous tax years.
If you received one of these letters and would like assistance, please contact me.