Welf, turning against the emperor, changes sides during the Investiture Controversy—supporting Pope Gregory VII as well as lending his support for the election of Rudolf of Rheinfelden as anti-king in March 1077.

Pope and emperor had been superficially reconciled in 1076, but the following year had seen them again engaged in active hostilities.

Henry, in consequence of these repeated acts of rebellion, declares Welf deposed in his newly acquired duchy.

However, supported by his faithful Bavarians, and aided by his father in Italy, Welf is able to maintain his place, and openly defy the ban of the empire in May 1077.

Welf joins the discontented princes who support he standard of Rudolph, at a time when any who refuse to follow the pope's direction can expect to be excommunicated by the church—a potent and effective threat in the social and political conditions of the time.