A group of Progressive rabbis have challenged the Chief Rabbi, Ephraim Mirvis, over his wish to restrict the entry of non-Jewish children into Jewish free schools .
Nearly 70 Reform and Liberal ministers wrote this week to the new Education Secretary Justine Greening, urging her to retain the current rules where only half of the places at a free school can be allocated on the basis of faith.
The Chief Rabbi has been lobbying for the removal of the 50 per cent faith cap, arguing that Jewish schools are most successful when they offer "a completely immersive Jewish environment".
However, the 68 signatories called on Ms Greening "not to abolish the 50 per cent admissions rule for faith-based free schools", saying they believed "Jewish values can happily co-exist with social cohesion".
Their intervention comes at a time when three groups are planning applications to open Orthodox Jewish secondary free schools in the London area in September 2018. In theory, under current regulations, up to half the intake for such a school could come from other faiths.
In response to news of the letter, a spokesman for Rabbi Mirvis said that he "has made his views on the current free schools model quite clear and we will continue to make our own representations to the government on this matter".
The letter to Ms Greening was orchestrated by Rabbi Jonathan Romain, of Maidenhead Synagogue, an opponent of separate faith schooling who stressed that the signatories also included faith school supporters.
It was signed by 67 Progressive rabbis or cantors including the chief executive of Liberal Judaism Rabbi Danny Rich and the co-chairs of its Rabbinic Conference, Rabbis Alexandra Wright and Richard Jacobi, as well as Rabbi Paul Freedman, chairman of the Assembly of Reform Rabbis UK. The lone Orthodox signatory was Rabbi Norman Solomon, a former minister at a number of regional synagogues.
The balanced approach of free schools, the letter says, enables children to have "both a sense of religious roots and openness to others. We feel it will benefit the children concerned and the society into which they will emerge and help shape".
Rabbi Romain said that approach was "now under threat. There is now a real danger that this progressive measure might be undermined".
Further calls for the lifting of the 50 per cent limit have come from the Catholic Education Service and the New Schools Network, a charity which advises faith school applicants.
The NSN's former director, Nick Timothy, was last week appointed as chief of staff for new Prime Minister Theresa May.
The Reform movement's Senior Rabbi, Laura Janner-Klausner, did not sign the letter as she was abroad.
Rabbi Romain said that only two Reform rabbis had chosen not to add their names, while he had not received a response from the two Masorti rabbis he had approached.
Meanwhile, Maurice Ashkenazi-Bakes, a supporter of one of the Jewish free school groups - the Hertforshire Jewish Free School - said this week that there was "a strong possibility" it would combine with another of the potential applicants, Kedem High School.
He said that he had been "astonished" to see that as many as 200 people had responded within 24 hours to a survey launched by HJFS to gauge demand.
The third applicant is the Barkai College group.
The Chief Rabbi has not supported any of the free school applications so far, instead preferring to explore options to create extra places at existing schools which, according to his office, would "avoid the challenges posed by the current free school model".