Thousands of ultra-Orthodox Haredi Jews rallied in Jerusalem's Sabbath Square to protest against mandatory recruitment to the Israeli Defence Forces (IDF).
The Knesset's Plesner committee is working on finding an alternative to the Tal Law, which exempts ultra-Orthodox students from the draft.
The Supreme Court declared the law unconstitutional. It is due to expire on 1 August.
"We must give our lives against the drafting of yeshiva students [to the army]," said Rabbi Shmuel Aurebach, one of the spiritual leaders of the Zionist Degel HaTorah political party. "In an issue that belongs to the heart of Israel, there are no compromises."
The demonstrators read verses from Psalms and performed prayers of lamentation in a public show of mourning.
National civilian service
According to the Tal Law, ultra-Orthodox men are excused military service for the purpose of religious study.
Some reports said that the committee will not recommend military conscription and may opt for drafting Haredi into a national civilian service, or fining those who refuse to be recruited.
"Instead of preparing the prisons for immigrants from Sudan, we suggest to those haters of religion to prepare 50,000 places of detention for yeshiva students who will refuse to be drafted," Pini Rosenberg, one of the speakers at the rally, said.
The Haredi are a small but active fringe ultra-Orthodox group that opposes the state of Israel.
Earlier this month, police accused them of defacing the Yad Vashem Holocaust memorial in Jerusalem with anti-Semitic graffiti.
More than 10 slogans painted in black, red and white were found in Warsaw Ghetto Square and on the memorial to Jews sent off to the Nazi death camps.
One slogan said: "Haredi World Committee."
Another said: "Thanks, Hitler, for the wonderful Holocaust you organised for us."