The ordination of a Bishop requires a pontifical mandate, that is, the official approval of the Pope. This requirement is a way of securing the unity of the Bishops with and under the Pope. Without such unity, the well-being of the entire Church is directly threatened. This papal mandate, a requirement of Canon Law (canon 1013), is so important that a Bishop who consecrates another Bishop without it, along with the one who is consecrated, is automatically excommunicated.
Even though the ordination of a Bishop requires the official approval of the Pope, an ordination of a Bishop without a pontifical mandate is valid; that is, the rank of episcopacy is conferred, but the ordination is illicit because it has not been carried out according to the prescriptions of Church law.
Only one Bishop is required for the valid ordination (or consecration) of a Bishop. Three Bishops are required for the licit consecration of a new Bishop, unless the Holy See dispenses from this as, for example, in countries where violent persecution of the Church is in progress. The requirement of three Bishops for licit ordination is a means of making clear the unity of the episcopate under Christ as present in each single consecration.
Bishops possess their power to ordain in virtue of their episcopal ordination; this means that every validly ordained Bishop, including those separated from union with Rome, has the power to ordain deacons, priests and Bishops, even in defiance of the Pope’s directives. When this happens, the Sacrament of Holy Orders confers rank and power in the name of Jesus and by His authority, and the Sacrament is valid. However, those Bishops who exercise their episcopal powers without the required pontifical mandate act illicitly. The unfortunate circumstances under which the Pope’s directives have been ignored have had historic consequences for the unity of the Catholic Church. Thus, the millions of Eastern Orthodox, as they call themselves, have for centuries ordained priests and Bishops without dependence on the Bishop of Rome. This, too, was the heart of the crisis since the Second Vatican Council, where the followers of Archbishop Lefebvre had Bishops ordained contrary to the expressed wishes of Pope Saint John Paul II.
There are some Churches separated from Rome whose priestly orders are questionable. The historic case of the Anglican Orders is worth noting here. In the document Apostolicae Curae(September 13, 1896), Pope Leo XIII declared Anglican Orders to be “absolutely null and utterly void.” The grounds for the declaration were twofold: the formula used in the ordination ceremony and the intention of the one performing the ordination. Not long after the Anglicans broke with Rome, they denied that the Mass is a sacrifice and, therefore, those whom they ordained were not ordained as priests to offer the Sacrifice of the Mass. (For Advanced Course lesson 23.)