"The authorities will face a united global ultra-Orthodox Judaism fighting for its soul," the spiritual leader of ultra-Orthodox Jews of European descent, Rabbi Dov Landau, told the community's leading newspaper Yated Neeman under the front-page headline "War".

The exemption of many ultra-Orthodox men from the military service performed by other Jews has long been a contentious issue in Israel but it has become more so as the Gaza war has dragged on, putting a strain on army reservists.

Prime Minister Benjamin Netanyahu's government has depended on the support of ultra-Orthodox parties for its majority in parliament.

But its failure to pass new legislation to give full-time seminary students continued exemption from military service has tested that support.

Both of the two main parties representing ultra-Orthodox of European descent have withdrawn their ministers from the government, while one has also stopped supporting it in parliament.

The ultra-Orthodox community represents 14 percent of Israel's Jewish population, about 1.3 million people, and around 66,000 men of military age previously benefited each year from exemptions.

The Israeli army announced in early July that tens of thousands of conscription orders would be sent out to ultra-Orthodox Jews.

Earlier this week, authorities arrested two brothers, both full-time seminary students, after they failed to heed their call-up papers.