Mich. Comp. Laws § 206.123: Sales other than sales of tangible personalty within state.

Sec. 123.

Sales, other than sales of tangible personal property, are in this state if:

The income-producing activity is performed in this state; or

The income-producing activity is performed both in and outside this state and a greater proportion of the income-producing activity is performed in this state than outside this state, based on costs of performance.