Benjamin Netanyahu, the Israeli prime minister, was forced to consider calling an early election on Tuesday after the largest party in the country's parliament walked out of his ruling coalition.
Just two months after joining a unity government, Shaul Mofaz led his Kadima party into opposition after failing to secure legislation extending conscription to Israel's ultra-Orthodox Jews.
Mofaz also resigned as deputy prime minister as negotiations over a new law on army service collapsed. "Kadima has decided to resign from the national unity government," Mofaz said.
"I committed that if we don't succeed in our mission we won't remain in the coalition. I'm keeping my word."
Holding 28 of the 120 seats in the Knesset, Kadima's entry into the coalition gave Netanyahu a majority virtually unparalleled in the history of the Jewish state.
Despite the loss of Kadima, the prime minister's Likud party will still hold an overall majority of 12 thanks to its alliance with smaller right-wing and religious parties.
But Netanyahu had appeared poised to call an early election in May shortly before he confounded observers by drawing Kadima into government.
Unwilling to yield to vote-winning concessions that smaller coalition partners are likely to demand when the next budget is drawn up in December, Netanyahu is likely to go to the polls early next year.
A general election is not due until October, 2013 but Netanyahu is highly popular in Israel and polls suggest that Likud would again form the next government.
Despite his strong position, Netanyahu will regard the loss of Kadima as a blow. Its support would have been useful domestically if he decided to launch unilateral military action against Iran's nuclear facilities.
Sinking fast in the opinion polls, Kadima had pinned its hopes of a recovery on securing reforms to the conscription law, which is viewed as highly unfair by the secular Israeli Jews who make up the majority of the population.
Until now, most ultra-Orthodox Jews have been exempt from army service on the grounds that many do not complete their religious education until they are in their forties.
With religious parties disproportionately powerful in the Knesset, as they can make or break coalition governments, Kadima - which takes a less combative line on negotiations with the Palestinians - is hoping to woo those angry over Netanyahu's reluctance to confront ultra-Orthodox leaders.
