This is a developing story and will be updated regularly.
Israel’s Supreme Court convened on Tuesday to begin considering whether to strike down a deeply contentious law that limits the court’s own power, in a hearing that sets the stage for a constitutional showdown between the country’s judicial and executive branches.
The high court is considering a bill passed by Parliament in July — pushed by the most nationalist and religiously conservative government in Israel’s history — declaring that judges could no longer overrule ministerial decisions using the legal standard of “reasonableness.”
The case is considered one of the most consequential in Israel’s history: Israelis from all political backgrounds say the country’s future and character partly depends on the hearing’s result. Justices could take until January to reach a decision.
The government of Prime Minister Benjamin Netanyahu sees the court as an obstacle to its vision of a more conservative, nationalist society. The court has historically acted as a check on religious influence on public life, some Israeli activity in the occupied West Bank, and decisions that favor Jews over Arabs.
The opposition considers the court a guarantor of Israel’s secular character, a protector of its minorities and a bulwark against authoritarianism.
The legislation passed in July was an attempt by the government to weaken the court: It barred the court from striking down government decisions on the grounds that they were “unreasonable.”
Coalition leaders said the concept — never defined in a statute — was too vague, and had in the past given unelected judges too much room to meddle in decisions by elected lawmakers. The coalition said that the court still had several other tools with which it could restrain the government.
Yariv Levin, the justice minister, said on Tuesday that the court’s decision to review the law was another example of it overstepping its remit, one that constituted “a mortal injury to the rule of the people.”
In a statement, Mr. Levin added that by seeking to rule on its own power, the court “places itself above the government, above Parliament, above the people and above the law. This situation is completely contrary to democracy.”
The court is hearing arguments from eight petitioners against the law, most of them civil society organizations that campaign for good governance, as well as representatives of the government and Parliament.
The law’s opponents argue that the legislation undermines Israeli democracy by limiting the power of the Supreme Court, which is the main check on government overreach. Israel has no written constitution and no second chamber of Parliament, increasing the court’s importance as a counterweight to the power of the cabinet and the legislature.
Eliad Shraga, who leads one of the groups petitioning against the law, said on Tuesday that the law was a kind of “regime coup.”
“This is a historical day, a historical event,” Mr. Shraga added, shortly before entering the courtroom with his sons. “I hope that it will be a red light to the regime.”
The law is one part of a wider legislative package, the rest of which the government has so far failed to implement. The government still hopes to pass another law that would give it greater control over who gets to be a judge. But Mr. Netanyahu has ruled out pursuing a third plan that would have allowed Parliament to overrule Supreme Court decisions.
The package has prompted what many see as the worst domestic political crisis in Israeli history, one that has widened longstanding rifts between secular and religious Israelis, as well as Jews of European and Middle Eastern descent.
Opponents of the law have held 36 consecutive weeks of mass protests. The judicial overhaul has also prompted some investors to divest from Israel, led more than 1,000 reserve soldiers to suspend their volunteer duty for the Israeli military, and strained Israel’s relationship with the United States government.
In a sign of how seriously the judiciary views the appeal, the chief justice, Esther Hayut, decided that all 15 of the court’s judges would hear the case — a record number that required rearranging the layout of the judges’ bench. Usually, between three and 11 judges sit for each case before the court.
In another sign of the case’s importance, lawmakers, foreign diplomats and broadcasters began lining up outside the courtroom at least 90 minutes before the start of the hearing to secure a seat. Some took selfies once inside.
Yitzhak Beret, legal adviser to Parliament, was the first person asked to speak by the judges — “a huge honor and privilege,” he said.
“I am truly emotional to be standing here today,” Mr. Beret added.
Legal analysts said it was far too early to determine how the court might rule. But from the judges’ opening questions and statements, it was clear that at least some members of the court had concerns about the law.
“It appears that you certainly believe that the duty to act reasonably also applies to the government and its ministers,” Justice Hayut said to Mr. Beret, the parliamentary adviser.
But if the court is barred from using the reasonableness standard, Justice Hayut added, “Who supervises that they do indeed act reasonably?”
Gabby Sobelman contributed reporting from Rehovot, Israel.