I don't normally publish anything from the SSPX, as their bishops are excommunicate and they are deeply unreliable in their theology. However, like a stopped clock, they got this one right:
Augustinian monks in Ireland have concelebrated Mass with Anglicans, thereby violating canon law and setting themselves up for canonical penalties.
Can. 900 §1. The minister who is able to confect the sacrament of the Eucharist in the person of Christ is a validly ordained priest alone.
Can. 908 Catholic priests are forbidden to concelebrate the Eucharist with priests or ministers of Churches or ecclesial communities which do not have full communion with the Catholic Church.
From Redemptionis Sacramentorum:
[172.] Graviora delicta against the sanctity of the Most August Sacrifice and Sacrament of the Eucharist are to be handled in accordance with the ‘Norms concerning graviora delicta reserved to the Congregation for the Doctrine of the Faith’, namely:
a) taking away or retaining the consecrated species for sacrilegious ends, or the throwing them away;
b) the attempted celebration of the liturgical action of the Eucharistic Sacrifice or the simulation of the same;
c) the forbidden concelebration of the Eucharistic Sacrifice with ministers of Ecclesial Communities that do not have the apostolic succession nor acknowledge the sacramental dignity of priestly Ordination;
d) the consecration for sacrilegious ends of one matter without the other in the celebration of the Eucharist or even of both outside the celebration of the Eucharist.
"[179.] Delicts against the faith as well as graviora delicta committed in the celebration of the Eucharist and the other Sacraments are to be referred without delay to the Congregation for the Doctrine of the Faith, which “examines [them] and, if necessary, proceeds to the declaration or imposition of canonical sanctions according to the norm of common or proper law”.
Here is +Cardinal Arinze's address:
His Eminence Cardinal Francis Arinze
Congregation for Divine Worship
and the Discipline of the Sacraments
00120 Vatican City State