[1] In 1869 he went to the Vatican Council as secretary to Cardinal Hohenlohe, and took an active part in opposing the dogma of papal infallibility, notably by supplying the opposition bishops with historical and theological material.
A sentence of excommunication was passed on Friedrich in April 1871, but he refused to acknowledge it and was upheld by the Bavarian government.
He continued to perform ecclesiastical functions and maintained his academic position, becoming an ordinary professor in 1872.
[1] In Bavaria, in 1882, the Minister of Public Worship, yielding to ultramontane pressure, transferred him from his chair in theology to the philosophical faculty as professor of history.
By this time he had to some extent withdrawn from the advanced position which he at first occupied in organizing the Old Catholic Church, for he was not in agreement with its abolition of enforced celibacy.