Are wages earned by a Michigan nonresident, while temporarily telecommuting from a location in Michigan, subject to tax in Michigan?

Yes, (except for residents of reciprocal states), a nonresident is taxed on all wages earned while physically present in Michigan.

Note: Residents of reciprocal states, who are working in Michigan, do not pay Michigan tax on their salaries or wages earned in Michigan. The following states have a reciprocal agreement with Michigan: Illinois, Indiana, Kentucky, Minnesota, Ohio and Wisconsin.