From: Rabbi Moshe Sofer
To: Rabbi David
A community accepted a new rabbi without the consent of their incumbent rabbi, Rabbi David, who held a formal appointment contract containing a written oath and cherem. The Chasam Sofer rules that if the community members verbally affirmed the oath it is clearly binding; even if they only signed the document without verbal articulation, he sides with the Chavos Yair that a written oath is fully binding, concluding that the community remains in violation until they obtain Rabbi David's consent.
Source: Shu"t Chasam Sofer YD §227