The High Court of Justice ruled on Thursday in favor of state recognition of private Orthodox conversions to Judaism and that those converted through this process should be eligible for Israeli citizenship under the Law of Return, in a decision Israel's chief rabbi blasted as "outrageous."

The decision by nine-justice panel headed by Court President Miriam Naor weakens the chief rabbinate and the official system of conversions, and strengthens the private rabbinical courts operating in the haredi and Zionist sectors.

The ruling also has possible repercussions concerning Reform and Conservative conversions which have thus far not been recognized by Israel.

"Restricting recognition of conversions to the official track alone, as the respondents suggest, will hurt the right to return (to Israel) which is a fundamental right of every Jew, and violates the instructions of the Law of Return," Naor wrote in her judgement.

In response, Sephardi Chief Rabbi Yitzhak Yosef blasted the decision as "outrageous," saying it was "inconceivable that the pirate conversion industry will be recognized by the state."

Rabbi Yosef added that "Israel operates its own conversion mechanism which operates with clear standards and is welcoming to all parts of the Israeli public, [the court's decision] is the de facto execution of official state conversion mechanism."

Conversions of immigrants are generally overseen by the chief rabbinate, within the framework of the Law of Return, which grants automatic citizenship to Jews. Most of those who undergo these conversions are Russian and Ethiopian immigrants not seen as Jewish under Orthodox law.

Occasionally, an exceptions board at the Interior Ministry permits foreign nationals to be converted through the rabbinical system as well.

The justices ruled on three appeals filed on behalf of foreign nationals who came to Israel as tourists and were later converted to Judaism by private rabbinical courts operated by the ultra-Orthodox.

The Interior Ministry refused to recognize these conversions and even made those who went through the process leave Israel once their visas expired.

The state had replied in its response to the appeal that the Law of Return applied only to those who converted while in Israel and by the official system overseen by the chief rabbinate.

Rabbi Gilad Kariv, head of the Israel Movement for Reform and Progressive Judaism said "the High Court ruling determines unequivocally that there is more than one way to convert in Israel."

"We expect the Israeli government to fully recognize reform conversions in Israel just as it for years has recognized such conversions when performed abroad," Kariv said.

"This is a day of celebration for all who believe that the unity of the Jewish people will come only through mutual respect and religious tolerance and by Israel's recognition of all streams of thought of the Jewish people."

Religious Services Minister David Azoulay (Shas) blasted the decision.

“The High Court is trying to undermine Israel’s Jewish foundations and is harming the state conversion system and the Chief Rabbinate,” he said. “Anyone who keeps silent about the High Court’s decision to recognize pirate conversions shouldn’t be surprised to find hundreds of thousands of non-Jews here in the State of Israel who have obtained citizenship under the Law of Return as the result of a dubious industry of fake conversions. I intend to work through legislation so that conversions in Israel will be exclusively those performed by the state conversion system.”

Meretz chairwoman Zehava Galon welcomed the court’s “dramatic ruling,” which “breaks the rabbinate’s monopoly and constitutes another step forward in the battle by different [Jewish] movements in Israel to be Jews in their own way, with no ranking of Jews as equal and more equal.”

She added that she hoped the ruling, which was handed down in the case of Orthodox converts, would also apply to non-Orthodox conversions.

MK Ksenia Svetlova (Zionist Union) similarly welcomed the breaking of the rabbinate’s monopoly and hoped the court would soon recognize non-Orthodox conversions as well.

MK Elazar Stern (Yesh Atid), who sponsored a bill to reform the conversion system in the previous Knesset, said the decision constituted “great tidings” for “the war on assimilation,” and especially for the hundreds of people who have already converted via alternative conversion courts. He termed the court’s ruling “a direct result” of the current government’s decision to abandon his proposed reform.