Mich. Comp. Laws § 141.645

Sec. 45. For the purpose of determining net profit allocable to the city under this ordinance, a corporate taxpayer may elect to file a consolidated return including subsidiaries whose voting stock is more than 50% owned by the taxpayer, if such return will more properly reflect the net profits and activities of the taxpayer in the city. The city may require a consolidated return if necessary to properly determine net profits of the taxpayer allocable to the city.