A new law on conversion to Judaism could lead to a full-blown coalition crisis in Israel.
The law, presented by Avigdor Lieberman's Yisrael Beiteinu, would allow each city's chief rabbi to perform conversions. The Charedi parties are threatening to leave Binyamin Netanyahu's government if the law is passed.
Yisrael Beiteinu promised in its election manifesto that it would introduce new laws to make conversion easier. Many of its voters are immigrants from the former Soviet Union and it is estimated that about 300,000 of these immigrants, while eligible for Israeli citizenship according to the Law of Return, are not regarded as Jewish by the Orthodox rabbinate.
Under the current system, only special conversion courts, many of which present very stringent demands to the potential converts, are allowed to perform conversions. The party wants to open this up to the local chief rabbis.
The new law, if passed, would also allow only the Chief Rabbi to annul conversions retroactively. Currently, any rabbinical court can annul conversions. One court's decision, a year-and-a-half ago, to annul thousands of conversions performed by one of the special courts, threw the whole giyur process into chaos.
As of last weekend, it seemed that the proposal would be voted smoothly through the Knesset. Yisrael Beiteinu MK David Rotem had discussed all the details with Sephardi Chief Rabbi Shlomo Amar and agreed in advance with the Shas leadership on their support.
But he reckoned without the other ultra-Orthodox party, United Torah Judaism (UTJ).
UTJ's spiritual leaders currently control most of the rabbinical courts through hardliner dayanim, or rabbinical judges, who follow their guidance. Rabbi Yosef Shalom Elyashiv, the most senior Charedi rabbi, is a staunch opponent of liberalising the conversion procedures. He and his colleagues fear that allowing local rabbis to perform conversions will allow many thousands of immigrants to become Jewish in a much easier - and to them, fraudulent - process.
UTJ pressured Shas and succeeded in convincing its leaders to join them in opposing Yisrael Beiteinu's proposal. Without Shas and UTJ in his coalition, Prime Minister Binyamin Netanyahu would lose his majority in the Knesset.
On Sunday, he appointed veteran religious lawyer Dr Yaakov Weinroth to try and mediate between the parties.
Dr Weinroth's first compromise proposal was turned down by both sides.
On Tuesday, the Yisrael Beiteinu leader Foreign Minister Avigdor Lieberman said that "we will make sure that the conversion law passes in the Knesset even if it does cause a coalition crisis. This has nothing to do with Torah or tradition, only with power struggles within the Charedi world."
On Wednesday, Moshe Gaffni, a UTJ Knesset member, said that the rabbis have given them orders to leave the coalition immediately if the law is passed.
Mr Lieberman said that he was adamant that he would bring the law to the Knesset before it begins its spring recess next week.
But it is not only the Charedi rabbis who are concerned about the law. Leaders of the Reform movement in Israel have also attacked another clause, which mandates that Israeli conversion will no longer be a basis for citizenship, and that only Jews from birth, their descendants, and those who have converted overseas, will be eligible under the Law of Return.