Johann Joseph Ignaz von Döllinger writes a letter to Archbishop of Munich Gregor Leonhard Andreas von Scherr in response to the archbishop's demand that Döllinger submit to the resolutions of the Vatican Council — including the resolution that papal infallibility is a dogma of the universal church. In his letter Döllinger refuses, which is no surprise because he has been arguing against papal infallibility for some time now.
He argues to the archbishop that the doctrine is contrary to everything the church has ever taught or stood for, concluding
"As a Christian, as a theologian, as an historian, and as a citizen, I cannot accept this doctrine."
The archbishop will excommunicate Döllinger, leading to waves of anger against the church and support for Döllinger. One important development will be the establishment of the Old Catholic Church movement in Germany via the Old Catholic Church in the Netherlands.
The Old Catholic movement claims to descend directly from the apostles and has communion with several churches around the world, including the Anglican Communion, but not the Roman Catholic church in the Vatican. Because Döllinger doesn't support the Old Catholic movement to the point of being ordained a bishop, the movement will lose a lot of steam. It still gets established, but the schism with the Vatican remains minor.