Apparently, the Department is waiting for a legislative fix that will remove this filing requirement for disregarded entities. The legislative delay appears to have motivated the Department to simply keep moving the deadline. The first deadline was June 30, 2011. It was then extended to October 31, 2011, and then December 31, 2011.
THE NOTICE AND FILING REQUIREMENT
According to the NOTICE, a person that is a disregarded entity for federal tax purposes, including a single member limited liability company or QSub, must file a separate return under the MBT or file as a member of a unitary business group if the requirements of MCL 208.1117(6) are satisfied. This requirement applies to all open tax periods under the MBT. A person disregarded for federal tax purposes that filed as a sole proprietor, branch, or division of its owner for MBT purposes (a "previously disregarded entity") is considered a non-filer for statute of limitations purposes under MCL 205.27a.
A person that previously filed an MBT return that included one or more previously disregarded entities, including a unitary business group, must amend its returns for all open periods, even if the amended returns do not result in a different tax liability.
A person required to file a return, or amend a return for a prior period, under this Notice must do so by July 1, 2012.
If your company has disregarded entities that are subject to this requirement - you may not have to file anything if you keep waiting.