Paulist Father Ron Roberson, associate director of the U.S. bishops' Secretariat of Ecumenical and Interreligious Affairs, said the split reveals disagreements on some "pretty significant issues" among more than a dozen Orthodox churches.

At issue is the role of the ecumenical patriarch in the Orthodox Church. The patriarch – currently Patriarch Bartholomew of Constantinople – has always been recognized as first among equals, with the authority to organize pan-Orthodox activities like international dialogue with the Catholics.

However, Russian Orthodox Church leaders do not believe Patriarch Bartholomew has the authority to interfere in the internal affairs of individual Orthodox churches. They say that is what he did when he granted canonical recognition to two independent Ukrainian Orthodox churches.

"It could be the beginning of a schism that would be long-lasting" if others follow the lead of Moscow, Father Roberson told Catholic News Service Oct. 16, the day after the decision was announced.

For instance, he said, the Serbian Orthodox Church has been supportive of Moscow's position.

"The question is, will they follow?" he asked. "Can they (Serbians) be in communion with Constantinople and Moscow at the same time, even if (Moscow and Constantinople) are not in communion with each other?"

It is "unknown what the implications will be," he said.

Father Roberson, who has written and updated "The Eastern Christian Churches: A Brief Survey," referred to a similar dispute in 1996 over the Orthodox in Estonia, a former Soviet Republic. The ecumenical patriarch reconstituted a church there over the wishes of the Russian Orthodox Church. In the end, he said, they agreed that Estonia would have a church under Constantinople and a diocese under the Moscow Patriarchate.

In Ukraine, for decades there have been three Orthodox churches: two self-declared autocephalous, or independent, and not considered canonical by the other Orthodox churches. The Ukrainian Orthodox Church in communion with the Moscow Patriarchate was considered canonical.

Earlier in October, in an effort to unify the Orthodox in Ukraine, the ecumenical patriarchate's synod recognized both independent churches as canonical churches and reinstated the heads of both as bishops in good standing.

The Ukrainian Orthodox Church-Moscow Patriarchate has said it has no desire to be independent from Moscow. Some people believe some of that church's bishops would go to the independent churches, Father Roberson said, adding, "That's pure speculation at this point."

In severing ties with Constantinople, Moscow said it would not participate in any international dialogues if the co-chair is a bishop of the ecumenical patriarchate.

"If Moscow and Constantinople will not sit down at the same table, then any theological dialogue would be with some of the Orthodox churches, not all of them," Father Roberson said. "If the Russians are missing, that is something like half of the faithful in the Orthodox world, which is very significant."