Israeli Vice Prime Minister Shaul Mofaz, the leader of the centrist Kadima party, could bolt Prime Minister Benjamin Netanyahu's Likud-led coalition as early as Tuesday due to sharp disagreement over legislation aimed at imposing military service on the country's ultra-Orthodox Jewish community.

A series of phone calls between lawyers representing both parties failed to yield a breakthrough in negotiations, and Mofaz was expected to hold a press conference later in the day.

"If nothing happens (to end the conflict with Likud), I believe it is a correct conclusion (that Mofaz would seriously consider quitting on Tuesday)," The Jerusalem Post quoted a Mofaz associate as saying.

"It is not an ultimatum. It is due to the fact that there is no progress," he added.

Early in May, Netanyahu and Mofaz shocked entire political spectrum with the announcement of a unity government deal, which brought aboard Kadima's 28 lawmakers, making for a massive 94- member coalition.

Kadima officials, who previously criticized Netanyahu's leadership skills, welcomed the move, saying that it would afford Netanyahu greater political stability while enabling their party to promote a host of domestic issues -- including mandatory military service for the country's religiously observant.

The partnership began to wobble amid a heated debate over a new draft bill, leaving Netanyahu scrambling in recent weeks to please all of his coalition partners and prevent a political crisis.

Two weeks ago, the prime minister dissolved the Plesner Committee he tasked with drafting a replacement to the so-called Tal Law, which allows religious seminary students to defer their conscription indefinitely and has long raised the ire of other sectors of Israeli society.

The Supreme Court earlier this year struck down the law and it is due to expire on August 1.

The disagreement between Likud and Kadima centers on a clause calling for punishments for both Jewish and Arab men who evade military or national service.

Netanyahu opposes imposing personal fines on draft dodgers, fearing a crisis with the ultra-Orthodox parties in his coalition. As well, versions of the bill that called for inducting Israeli Arabs into the military or national service angered leaders of some Arab parties.

Following the disbandment of the Plesner Committee, sources in Kadima threatened to quit the coalition if Netanyahu fails to pass a draft law that would meet their standards.

"We're not afraid to return to the opposition," Mofaz' colleagues said at the time. "(Netanyahu) cannot pass a bill without Kadima, so the prime minister has to decide between a covenant with haredim (ultra-Orthodox Jews), and being everyone's prime minister. We call the sanctions personal responsibility."

On Tuesday, Mofaz's associates slammed Netanyahu for expressing optimism at a Likud faction meeting the previous day, in which he contended that the differences could soon be bridged and that he hoped to pass a bill in parliament by the end of the month that would see a "huge rise" in ultra-Orthodox and Arab enlistment.

"I don't know where his optimism comes from," said one Kadima official, adding "optimism has to be based on something concrete. No headway has been made," according to the Post.

While the Knesset parliament is scheduled to begin its three- month recess on July 25, Speaker Reuven Rivlin said on Monday that he would delay the recess to enable the government to pass a bill to replace the Tal Law.