When Israeli Supreme Court judges overruled a decision by Prime Minister Benjamin Netanyahu in January to award the Finance Ministry to an ally convicted of tax fraud, some of the justices used a contentious legal concept to block the move.

The appointment was “unreasonable,” they said.

When judges struck down Mr. Netanyahu’s appointment in 2015 of a new deputy health minister, they used the same legal argument.

Unreasonable.

And the decision by an earlier Netanyahu government, in 2012, to reject a particular candidate for the directorship of the tax authority?

That was unreasonable, too.

It is these kinds of judicial interventions — using the subjective legal concept of “reasonableness” — that are at the center of what is widely seen as the gravest domestic crisis in the history of Israel. Mr. Netanyahu’s coalition is close to passing a new law that would prevent the Supreme Court from using the concept of reasonableness to overturn government decisions.

Since mass protests in March, the coalition has suspended other plans to allow Parliament to overturn the court’s decisions and give the government more control over the selection of the court’s judges. Though the opposition fears that these plans could be revived, the government has no means of enacting them until the winter session of Parliament in October.

For the time being, the coalition is only proceeding with a law to limit the court’s use of “reasonableness,” but that move alone has been enough to return Israeli society to the brink.

In recent days, doctors have gone on strike in protest, raising the specter of a shutdown to the health system, even if their action lasted just two hours on Wednesday. Military reservists have started to withdraw from volunteer duty, threatening Israel’s defense capacity. And tens of thousands of protesters are regularly shutting down roads and infrastructure, leading to widespread fears of armed conflict between the government’s critics and supporters.

Opponents of the government’s proposal view the legal concept of reasonableness as a crucial protection against government overreach, and a key pillar of Israeli democracy. In particular, they fear that the current government — an alliance of ultraconservatives and ultranationalists — might use reduced judicial oversight to help mold a more religious and less pluralist society, principally by awarding jobs and funds to pet projects and allies, and firing officials who oppose them.

“This is about whether the resources of the state will actually be used for the public interest,” said Amichai Cohen, a legal expert at the Israel Democracy Institute, a Jerusalem-based research group. “Will the ministers interpret this elimination of reasonableness as carte blanche to just use the resources at their disposal, as they see fit, for political reasons?”

Supporters of the measure, which Parliament is expected to vote on next Monday, present it as a boon for democracy: a modest limit on the ways in which an elected government can be stymied by unelected judges, who will in any case still have other tools to overrule ministers.

“Israel will continue to be a democratic state,” Mr. Netanyahu said in a speech Thursday. “It will continue to be a liberal state.”

To Daniel Friedmann, a law professor and former justice minister, the reasonableness concept allows judges to assume too much executive power from officials and ministers, instead of merely acting as a check on government decisions.

“In reality, it enables the court to replace all other authorities,” Mr. Friedmann said. “The scope of action should be narrowed.”

The concept of reasonableness has become so contentious in part because it was never defined in a law passed by Parliament. Instead, its definition and application were developed by judges over several decades since the 1960s. Versions of the concept are used by courts in Australia, Britain and Canada, among others.

In Israel, judges generally consider a decision unreasonable if they conclude it was made without considering all relevant issues or without giving relevant weight to each issue, or by applying too much weight to irrelevant factors.

The Supreme Court has used the standard to oppose the appointment of senior civil servants who had been involved in covering up the extrajudicial killing of Palestinian militants. The court also cited the standard when it ruled that the government should do more to fortify classrooms against rocket fire from the Gaza Strip. It also used it to order a municipal council to build a Jewish ritual bath and to force the dismissal in 1993 of a minister, Aryeh Deri, who had been indicted on corruption charges.

Though “reasonableness” has been wielded against governments of all political stripes, Mr. Netanyahu’s coalition perceives it as a particular challenge to its authority.

After Mr. Deri returned to government earlier this year, judges said that it was unreasonable for him to be appointed to lead three ministries — including the treasury — because of his long history of corruption convictions. The judges said it was particularly unreasonable given that Mr. Deri, a veteran ultra-Orthodox lawmaker, had reneged on a plea deal he signed in his most recent corruption trial in 2021, which the judges interpreted as a pledge by Mr. Deri to quit political life.

Mr. Deri says he never promised to leave political life entirely, only to quit Parliament briefly; the deal’s ambiguity was widely reported at the time.

In 2015, the Supreme Court said it was unreasonable for Mr. Netanyahu to allow Yaakov Litzman, another ultra-Orthodox lawmaker, to effectively run the health ministry while serving as deputy health minister. At the time, Mr. Litzman was wary of accepting too senior a role in a state that many ultra-Orthodox Jews do not formally recognize.

In 2012, the court ruled it had been unreasonable for the Netanyahu government to refuse to appoint a particular candidate for the directorship of the Israeli tax authority. The rejected candidate had been nominated by an expert panel, and “stood out for his extraordinary professionalism and extensive education,” the court said.

Researchers say that the court has not used the standard as often as its critics claim, and is in fact more likely to throw out petitions to fire government officials than uphold them.

Over the past decade, the court has rejected petitions — made by private individuals, civil society groups or political parties — to fire three ministers in Mr. Netanyahu’s earlier cabinets, including a previous petition to fire Mr. Deri in 2015.

Since 2003, the court has rejected 52 of the 64 petitions that it received to strike down a government appointment on the basis of reasonableness, according to recent research by Tachlith, a Tel Aviv research group. Of the 12 petitions that the court upheld, only seven were upheld using the reasonableness standard, according to Tachlith.

As a result, some argue that the concept’s biggest impact is invisible and unquantifiable: It forces ministers to consider whether their decisions would survive a subsequent inquiry by the Supreme Court — meaning that its effect is felt most in the minister’s office, before a decision is taken, rather than afterward in the courtroom.

“You don’t want to do something that will be dismissed by the court,” said Natan Sharansky, a former deputy prime minister who headed four ministries in the 1990s and 2000s.

As a result, ministers often consult lawyers before taking a decision, Mr. Sharansky said. “Usually, you ask for advice: What is the chance that it will be appealed in the court and what are the chances that the court will say that it’s not reasonable that you’re doing this or this?”

To critics of reasonableness, this is a problem: It could prevent ministers from carrying out what voters elected them to do. To supporters of the standard, it’s a benefit: It deters ministers from acting in a corrupt or irrational way.

Mr. Sharansky said the concept was too broad and that, in principle, he supported the government’s plan to narrow its application.

But after the plan set off an increasingly toxic national discourse, he grew concerned about the way the issue had divided society.

“I really believe that it was something which could be useful, but the way it was presented and how it was pushed ahead made it almost impossible,” he said. “The real drama is not in specific proposals. The real drama is the fact that there is no serious mutual discussion.”

Gabby Sobelman contributed reporting from Rehovot, Israel, and Hiba Yazbek from Jerusalem.