Israel’s supreme court justices have begun hearing petitions against a key part of the rightwing government’s judicial overhaul limiting the court’s powers, a development that could trigger an unprecedented constitutional crisis. For the first time, a panel of all 15 judges convened on Tuesday to discuss eight filings aimed at striking down the “reasonableness” clause, passed by the Knesset in July, which abolished the supreme court’s ability to overrule government decisions. The hearings put the country’s top judges in the position of deciding on their own roles. The government has indicated it will not comply if the court strikes down the law, which would mark the first time it had overturned a semi-constitutional “basic law”. Such a move would plunge Israel into uncharted political and legal waters; the figurehead president, Isaac Herzog, has repeatedly warned of civil war. Protesters gathered outside the court building in Jerusalem as the hearing began, banging drums, blowing whistles, chanting and waving Israeli flags. In the hundreds, they were later joined by several dozen rightwing activists, who shouted “the people are the sovereign” and held signs declaring they had voted for the prime minister, Benjamin Netanyahu, and not the supreme court’s chief justice, Esther Hayut. “We are already in a constitutional crisis: government ministers have made no secret of their intentions to remove gatekeepers such as the attorney general and instead nominate people who will protect them,” said Noa Sattath, the executive director of the Association for Civil Rights in Israel, which filed an amicus brief to the supreme court along with 37 other human rights organisations. “The supreme court says it will only strike down a basic law in exceptional circumstances. Our argument to the justices is that they need to look at the full picture here, not just a case by case basis. The sum total of these changes and laws from the coalition will undermine our democratic structures.” A ruling could be passed down at any time within the next four months, but the opening session of the hearing was watched closely for initial clues about which way the justices will lean. It comprises both liberal and conservative judges. Addressing the government’s legal representatives, Hayut said: “It’s clear you think that the duty to act reasonably applies to the government and its ministers … But who makes sure they indeed do so?” At the behest of his new coalition partners, Netanyahu introduced a package of sweeping judicial changes when he returned to office in December. The legislation is aimed at curbing the influence of the supreme court, which the Israeli right has long alleged is biased and too powerful for an unelected body. The planned changes, including limiting the court’s ability to overturn laws and giving politicians more control over judicial appointments, have been denounced by critics as a transparent power grab that will erode democratic norms and aid Netanyahu’s fight against corruption charges, which he denies. The “reasonableness” clause was the first element of the judicial overhaul to pass into law, despite eight months of sustained opposition from the biggest protest movement in Israel’s history. The proposals have split Israel along lines of religion, ethnicity and class, thrown the military into chaos, damaged the shekel, and led to public concern for the country’s democratic health from key allies such as the US. In the next few weeks, the supreme court is also due to hear petitions against two more bitterly contested pieces of legislation passed by Netanyahu’s coalition of rightwing and religious parties that critics say are designed to protect the position of the prime minister and his political allies. “The very discussion about the possibility of striking down basic laws, which are the top of the legal pyramid in Israel, and the possibility of declaring the prime minister incapacitated, are mortal damage to a government by the people,” the justice minister, Yariv Levin, the architect of the judicial proposals, said on Tuesday morning. “The court, whose judges elect themselves behind closed doors and without a protocol, has set itself above the government, above the Knesset, above the people and above the law… … That situation is completely contrary to democracy. It means a court without checks and balances at all.” Compromise talks between the government and opposition parties brokered by Herzog have repeatedly ended in stalemate, but before Tuesday’s hearing Israeli media reported new attempts behind closed doors. Netanyahu said on Monday he aimed to “reach a national consensus to restore the balance of power” between the branches of government. He has not stated whether he will respect a supreme court decision to overturn the law scrapping the “reasonableness” clause.