The Canon that Nicholas cited (I believe from the Apostolic Canons) poses some interesting problems.
Strictly speaking, it calls for deposition (for the cleric involved to be kicked out of their office) - yet such a deposition requires action be taken either by his superior, or in the case of a Bishop, by his Synod (at least as far as I'm aware.)
Realizing this, some might say "well, that hasn't happened, so keep trucking and just try to ignore what these ecumaniacs are doing."
However, let's think carefully about this. The reason this ancient canon exists in the first place (and the reason why all disciplinary canons exist) is because it is defending a truth - the doctrinal issues in this case being the unity of the Church, Her visibility, the spiritually venemous (and contageous) nature of heresy and that heresies do not inherit the Kingdom of God (and that "churches" which are characterized by the acceptance of such falseness are no churches at all.)
While there are much more explicit statements/documents emminating out of "world Orthodoxy" which clearly condemn their ecumenistic communion, the total failure of the various local churches to expell offending heirarchs/clergy from their offices (indeed quite the contrary, officially such activities are praised and encouraged, particularly when it is the president of these local churches or senior heirarchs and representatives who are involved) has to say something. While the failure of a local church to discipline a Bishop who makes a mockery of the canons is one thing, this endemic problem of the ecumenist "churches", which is not only not condemned but even flattered, is quite another. This anti-canonical activity cannot but betray underlying attitudes and beliefs. This is only confirmed by much more overtly/explicit acts of spiritual treason (like the various agreed statements put out by the ecumenists with the approval of their local churches, or grave acts like pretending to "lift" the Church's anathemas of heresy or ignoring ecumenical councils and affecting material communion with condemned heresy.)
People can shout "extremism" or "fanaticism" all they want, but I have to pose two questions to such persons.
Just what exactly constitutes grounds for breaking with heirarchs who attempt to destroy the Church; are we to wait until they start sacrificing virgins upon the altar, or replace the Holy Icons with cartoon stills? Honestly, I think for many, a Bishop putting a moratorium on ethnic festivities would get more of a reaction (in terms of threats of witholding eucharistic communion and fraternal ties) than any attack upon the dogmas of the Church.
Honestly, which of the Great Fathers of the Church could they ever imagine having any part in the activities of the ecumenists, or who would react with indifference to them? I have a very hard time imagining St.Mark of Ephesus not withdrawing fellowship with Patriarch Athenagoras or his successors, after the suppoed "lifting" of the Church's anathemas against Papism. I cannot see any of the ancient Fathers simply shrugging their shoulders, after hearing of the activities of the Antiochians in regard to the "Non-Chalcedonians." I'm afraid that too much of "our" thinking these days has been conditioned by the assumed legitimacy of "pluralism" in all areas of life, including matters of religion to varying degrees. Ideas as such really are not considered important - pragmatism, and sentimental notions of peace and "luv" seem to paramount. While this may be the legacy of philosophical modernism/radical skepticism and practical atheism/agnosticism, it is not the legacy of Orthodoxy. It's certainly not the legacy of the great confessors and martyrs of the Church.
Seraphim