http://www.novusordowatch.org/sspx_dossier_sede.pdf20. Firstly, the refusal to name the Vatican II “Popes” in the Canon of the Mass.
5.1.
Mass Una cuм: Bishop Guérard des Lauriers used to say that
"to cite John Paul II at the Te Igitur of the Holy Mass is to commit, objectively and ineluctably, the double crime of sacrilege and capital schism.” On the contrary, the expression Una cuм in the Canon of the Mass does not mean that one affirms that he is ‘in communion’ with the erroneous opinions of the Pope, but rather that one wants to pray for the Church ‘and for’ the Pope, her visible head. In order to be sure of this interpretation, let us report the rubric of the missal for the occasion of a bishop celebrating Mass. In this case, the bishop must pray for the Church “Una cuм... me indigno famulo tuo”, which does not mean that he prays ‘in communion with... myself, your unworthy servant’ (which doesn’t make sense!), but that he prays ‘and for... myself, your unworthy servant.’ We should then consider that those who refuse to name the Pope during the canon of the Mass think that the Church lost her visible head. This attitude is schismatic!
a) Fr. Boulet is quote right about the meaning of the so-called
“una cuм” clause of the Mass. This is indisputable, and I am not aware of any of Bishop Guerard’s followers who still maintains the erroneous exegesis of it. Which is not to say that they disown his conclusion. They do not. They maintain that a priest ought not to name
as Pope in the Canon of the Mass a man that is in fact not Pope. This is surely an entirely reasonable position to take. The only alternative is to admit the legitimacy of lying.
b) In any case, all know that it is
not schismatic to reject the claim of a Pope which one considers to be at best doubtful, so that Fr. Boulet’s comment, “this attitude is schismatic!” is incorrect and actually unjust.
Finally, one cannot consider as schismatics those who refuse to obey the Roman Pontiff because they would hold his person suspect or, because of widespread rumours, doubtfully elected (as happened after the election of Urban VI), or who would resist him as a civil authority and not as pastor of the Church.
[Wernz-Vidal, Ius Canonicuм [Rome: Gregorian 1937], 7:398.]