From Instruction Redemptionis Sacramentum:
"[169.] Whenever an abuse is committed in the celebration of the sacred Liturgy, it is to be seen as a real falsification of Catholic Liturgy. St Thomas wrote, "the vice of falsehood is perpetrated by anyone who offers worship to God on behalf of the Church in a manner contrary to that which is established by the Church with divine authority, and to which the Church is accustomed".
[170.] In order that a remedy may be applied to such abuses, "there is a pressing need for the biblical and liturgical formation of the people of God, both pastors and faithful", so that the Church's faith and discipline concerning the sacred Liturgy may be accurately presented and understood. Where abuses persist, however, proceedings should be undertaken for safeguarding the spiritual patrimony and rights of the Church in accordance with the law, employing all legitimate means.
[171.] Among the various abuses there are some which are objectively graviora delicta or otherwise constitute grave matters, as well as others which are nonetheless to be carefully avoided and corrected. Bearing in mind everything that is treated especially in Chapter I of this Instruction, attention should be paid to what follows."
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.