Protestants at Catholic Mass?

In My Humble Opinion
41

Nah, that is the standard language in the missalette which most churches get. It’s inside the front cover - guidelines for receiving Communion.

For Catholics
As Catholics, we fully participate in the celebration of the Eucharist when we receive Holy Communion. We are encouraged to receive Communion devoutly and frequently. In order to be properly disposed to receive Communion, participants should not be conscious of grave sin and normally should have fasted for one hour. A person who is conscious of grave sin is not to receive the Body and Blood of the Lord without prior sacramental confession except for a grave reason where there is no opportunity for confession. In this case, the person is to be mindful of the obligation to make an act of perfect contrition, including the intention of confessing as soon as possible (canon 916). A frequent reception of the Sacrament of Penance is encouraged for all.

For our fellow Christians
We welcome our fellow Christians to this celebration of the Eucharist as our brothers and sisters. We pray that our common baptism and the action of the Holy Spirit in this Eucharist will draw us closer to one another and begin to dispel the sad divisions which separate us. We pray that these will lessen and finally disappear, in keeping with Christ’s prayer for us “that they may all be one” (Jn. 17:21).

Because Catholics believe that the celebration of the Eucharist is a sign of the reality of the oneness of faith, life, and worship, members of those churches with whom we are not yet fully united are ordinarily not admitted to Holy Communion. Eucharistic sharing in exceptional circumstances by other Christians requires permission according to the directives of the diocesan bishop and the provisions of canon law (canon 844 Section 4). Members of the Orthodox Churches, the Assyrian Church of the East, and the Polish National Catholic Church are urged to respect the discipline of their own Churches. According to Roman Catholic discipline, the Code of Canon Law does not object to the reception of Communion by Christians of these Churches (canon 844 Section 3).

For those not receiving Holy Communion
All who are not receiving Holy Communion are encouraged to express in their hearts a prayerful desire for unity with the Lord Jesus and with one another.

For non-Christians
We also welcome to this celebration those who do not share our faith in Jesus Christ. While we cannot admit them to Holy Communion, we ask them to offer their prayers for the peace and the unity of the human family.

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Beeing born and raised in ancient Yugoslavia as a catlick (agnostic now), that is what they told me at catlick edu: Thou should go to catlick church every Sunday. If not available, chose orthodox one. If even that not available, go to mosque. Really. (That was originally intended, i believe, for conscripts sent all over the country).

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The Orthodox Church forbids its own members from taking communion in non-orthodox churches.

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Interesting conjunction of influences!

I was at a Catholic wedding where one of the Protestant guests went up and joined the communion line. Nobody seemed to mind, although the priest, almost certainly, didn’t know. The guy approached the ritual with all due respect – he is a Christian, after all – and it’s awfully hard to imagine any kind of harm being done.

(As an atheist, I was willing to stand up, sit down, stand up again, sit down again – the Priest himself joked that it was “Catholic aerobics” – but I did refrain from giving voice to any of the response, even the simplest “Amen.” Wouldn’t have been honest. It wasn’t noticeable by any means, so, again, no harm.)

ETA: (I was once at dinner at a friend’s house, and nobody had warned me that grace would be said before the meal. I sat perfectly still, not bowing, just leaden, waiting for it to be over. It was very embarrassing, but I did not feel I could, in all integrity, bow my head. Call me a stiff-necked atheist.)