AMONG the three main forms of contemporary Judaism (Reform, Conservative and Orthodox) one big point of difference has to do with the terms on which newcomers are received into the faith. And that difference isn’t just a religious debating point; it is a hotly contested political issue in Israel, and it has implications for the way Israel functions and understands itself as a state. A few background points. All Jews inherit a certain wariness of converting others to their creed. They associate religious proselytising with dark eras when they were on the receiving end of murderous campaigns to make them switch belief. But there are plenty of people who want to become Jews, and those aspirations have to be dealt with somehow.

In the 20th century, responses to this question have diverged. The Reform and Conservative streams of Judaism have sought to open the faith’s ranks by adopting more user-friendly and streamlined conversion procedures. The reaction of Orthodox rabbis has been to raise the bar even higher.

This matters a lot because the Orthodox have always controlled Israel’s Chief Rabbinate, the sole Jewish religious agency recognised by the state; and the institution has recently come under the sway of the ultra-Orthodox, religious purists whose political influence is out of proportion to their numbers. That means that an exceptionally strict school of Judaism holds the gateway to marriages, divorces and the conversion rites that are often a prerequisite for religious nuptials.

Israel has no civil marriage, though it recognises such ceremonies if conducted in other countries; so couples who want to wed but don’t qualify for a religious rite (perhaps because one partner is not recognised as Jewish) have to do so abroad.

For Orthodox Jews, conversion is an arduous process, typically taking years of study and ritual observance, until it is ratified by a court of three rabbis. Potential converts have no assurance that it will culminate in a conversion ceremony, which includes a ritual bath (pictured). Yet this remains the only path to full recognition as a Jew in the Jewish state.

In recent weeks, a move within the world of Orthodox Judaism to defy the authority of the Rabbinate and make conversion easier has become more visible. The ultra-Orthodox, meanwhile, have used their political influence to stop the Israeli state giving any ground to the more lenient line.

On August 10th, it was announced that a group of Orthodox rabbis had formed an independent conversion court and performed six conversions of minors. This amounted to open defiance of the Rabbinate. And last weekend, more details of the rebellion came to light: it emerged that the independent group had performed more than 50 secret conversions over the past few months, involving adults as well as children, as well as some marriages.

On the surface, the difference between the rebels and the Rabbinate is over a relatively minor point of theology. Orthodox conversion requires the prospective Jew to commit to a lifestyle observant of religious commandments. Where the rabbis differ is over how strict this requirement must be and to what degree it should apply to minors.

Underneath the theology, there is a power struggle. For the ultra-Orthodox, running the Rabbinate and laying down a strict line on admission to the faith is a vital way of maintaining a centralised kind of control over religious life in Israel. In many people’s view, this centralisation is at odds with older Jewish traditions. For centuries, conversion was a locally-regulated affair and rabbis in different places had a fairly wide remit to interpret the Talmud and the accumulated body of practice according to their own lights.

The fact that the “rebel rabbis” insist they can remain within the Orthodox camp while relaxing conversion rules poses an acute and direct challenge to the new, more centralised kind of authority. Modern communications affect this struggle in two contrasting ways. On one hand, independent-minded rabbis can keep abreast of one another’s ideas and practices more easily; on the other, it is now easier for the Rabbinate to keep on eye on what is happening, in Israel and across the world, and react accordingly.

The Rabbinate has placed rabbis in other countries whom they consider too lenient on a blacklist. Their converts arrive in Israel only to discover that they are not considered Jewish.

As of now, it is the Rabbinate that holds the political cards, given the influence of the ultra-Orthodox over Israel’s ruling coalition. But if the rebel movement gains more and more public support, at the expense of an unpopular religious establishment, that will eat away at the authority of the Rabbinate from within. If ordinary Israelis and diaspora Jews openly ignore its decrees, the ability of the Rabbinate to regulate Jewish life could be hugely compromised.

And that in turn could lay bare some other fault-lines within Orthodox Judaism, as well as Judaism as a whole. Expect to hear louder arguments over a wide range of sensitive issues, including homosexuality; the role of women in religious life; and the legitimacy of secular research in rabbinical studies. The rabbis' rebellion over conversion could become a harbinger of an even wider rift.