Friedrich, however, refused to take the oath approving the Council of Trent (the so-called Professio fidei Tridentina), not on religious grounds, but because he saw it as an affront to a reigning sovereign.
Although he was frequently denounced as a secret Protestant in the circles around the pope (one of his predecessors, his uncle Hermann of Wied, had in fact converted to Protestantism), Friedrich rebuffed efforts by Protestant princes to have him introduce Protestantism in the Electorate of Cologne.
Pope Pius V continued Pius IV's policy of refusing to confirm Friedrich as Archbishop of Cologne if Friedrich would not swear the Professio fidei Tridentina and threatened to withdraw the cathedral chapter's right to select the Archbishop of Cologne.
Friedrich traveled to the papal court in Rome to seek confirmation of his election, and was granted an extension of time until 25 November 1567.
After great pressure was applied by the representative of Emperor Maximilian II, Friedrich finally resigned on 24 October 1567.