When the deal establishing a new prayer area at the Western Wall was announced in January, it seemed to be pass without too much fuss.

The Charedi parties registered their opposition to making any concessions to the Reform and Conservative movements but, since the agreement preserved the strictly-Orthodox control of the main Kotel plaza, they were content to leave it at that.

But as the leaders of the progressive streams hailed the agreement as "historic recognition" of non-Orthodox Judaism and the Charedi media launched a hysterical tirade against the Reform "destroyers", a crisis became almost inevitable.

Six weeks later, Prime Minister Benjamin Netanyahu is under severe pressure from the two main religious parties in his coalition - Shas, led by Interior Minister Aryeh Deri, and United Torah Judaism, headed up by Health Minister Yaakov Litzman.

They are demanding legislation that will make it clear that their version of Orthodoxy is the only recognised form of Judaism in Israel. Meanwhile, the US Reform and Conservative movements are warning Mr Netanyahu that such a move would result in an irrevocable rift with the diaspora.

A year since the election, this crisis is the first serious threat to Mr Netanyahu's coalition. In an attempt to stave it off, on Monday Likud sources began to talk about the possibility of Isaac Herzog's Zionist Union joining the coalition.

Such a development would immediately diminish the Charedi parties' power over the prime minister. But they have been in Netanyahu coalitions before, are familiar with that trick and dismissed the rumours.

Mr Netanyahu has one factor working in his favour. The Charedi parties know they are unlikely to have more influence in another government and therefore do not want early elections. At the same time, the American rabbis do not want a crisis with Israel, especially with political turmoil at home.

But finding a compromise will be tricky: the Charedim refuse to even recognise the non-Orthodox streams as a party they can compromise with.

A further complication is the High Court ruling that local religious councils - which are all controlled by the Orthodox - must allow Reform and Conservative members to use public mikvaot. The Charedi parties have already tabled legislation to circumvent this decision.

Ultimately, they hold a strong hand and the solution will have to reflect that. Mr Netanyahu may need all the support he can get in the US, but Shas and UTJ can bring down his government - and survival trumps all.