43 We are aware that those who thus belittle obedience in order to justify themselves with regard to those functions which they have unrighteously assumed, defend their position by recalling a usage which prevailed in ages past. Yet everyone sees that all ecclesiastical discipline is overthrown if it is in any way lawful for one to restore arrangements which are no longer valid because the supreme authority of the Church long ago decreed otherwise. In no sense do they excuse their way of acting by appealing to another custom, and they indisputably prove that they follow this line deliberately in order to escape from the discipline which now prevails and which they ought to be obeying.
Source: Ad Apostolorum Principis (Vatican.va)