The company confirmed it was re-evaluating its four-year relationship with Dentsu Aegis Network in a statement to AdAge.
In 2014, Microsoft hired Interpublic to handle its advertising work and Dentsu Aegis Network to manage its global media account.
Media planning has been handled since then by a cross-discipline team from Dentsu Aegis agencies, led by Carat.
Dentsu Aegis Network declined to comment.
Campaign has contacted Microsoft and is waiting for a response.