Israel's Supreme Court ruled on Tuesday that the government must draft ultra-Orthodox Jewish seminary students to the conscript military, a decree likely to send shockwaves through Prime Minister Benjamin Netanyahu's coalition.

Netanyahu's coalition relies for its survival on two ultra-Orthodox parties that regard longstanding conscription exemptions as key to keeping their constituents in religious seminaries and away from a melting-pot military that might test their conservative customs.

The ultra-Orthodox conscription waiver has become especially charged as Israel's armed forces, made up mostly of teenage conscripts and older civilians mobilised for reserve duty, are overstretched by a multi-front war, in Gaza and Lebanon.

"At the height of a difficult war, the burden of inequality is more than ever acute," the court's unanimous ruling said.