Hello Steve,
This
following is (or should be) published in your church Missalette…
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 § 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 § 3). **
Canon 844 says the following …
§3 Catholic ministers may lawfully administer the sacraments of penance, the Eucharist and anointing of the sick to members of the eastern Churches not in full communion with the catholic Church, if they spontaneously ask for them and are properly disposed. The same applies to members of other Churches which the Apostolic See judges to be in the same position as the aforesaid eastern Churches so far as the sacraments are concerned.
This does not really explain the justification for allowing Orthodox to partake, but it clearly states that they may do so. There are no conditions mentioned here, however the USCCB further states (above) that the individuals interested " … are urged to respect the discipline of their own Churches." It does not state that they are required to respect the discipline of their own churches, the invitation appears to be an open one.
I find it interesting that the PNCC and the Orthodox churches both specifically reject the Papal dogmas of 1870AD, yet this exception is offered to them. Roman Catholics in otherwise good standing who deny the Papal dogmas are excommunicated latae sententiae and they are anathematized.