JERUSALEM — Tens of thousands of protesters marched into Jerusalem on Saturday evening and hundreds of thousands of Israelis took to the streets in Tel Aviv and other cities in a last-ditch show of force aimed at blocking Prime Minister Benjamin Netanyahu's contentious judicial overhaul.

Also Saturday, more than 100 of Israel's former security chiefs signed a letter pleading with the Israeli premier to halt the legislation, and thousands of additional military reservists said they would no longer report for duty, in a protest against the plan.

In scorching heat that reached 33 C (91 F), the procession into Jerusalem turned the city's main entrance into a sea of blue and white Israeli flags as marchers completed the last leg of a four-day, 70-kilometer (45-mile) trek from Tel Aviv to Israel's parliament.

The marchers, who grew from hundreds to thousands as the march progressed, were welcomed in Jerusalem by throngs of cheering protesters before they set up camp in rows of small white tents outside the Knesset, or parliament, before Monday's expected vote. Meanwhile, hundreds of thousands flooded the streets of the coastal city of Tel Aviv, the country's business and cultural capital, as well as in Beersheba, Haifa and Netanya.

Netanyahu and his far-right allies claim the overhaul is needed to curb what they say are the excessive powers of unelected judges. But their critics say the plan will destroy the country's system of checks and balances and put it on the path toward authoritarian rule.

U.S. President Joe Biden has urged Netanyahu to halt the plan and seek a broad consensus.

The proposed overhaul has drawn harsh criticism from business and medical leaders, and a fast-rising number of military reservists in key units have said they will stop reporting for duty if the plan passes, raising concern that the country's security interests could be threatened. An additional 10,000 reservists announced they were suspending duty on Saturday night, according to "Brothers in Arms," a protest group representing retired soldiers.

More than 100 top former security chiefs, including retired military commanders, police commissioners and heads of intelligence agencies, joined those calls on Saturday, signing a letter to Netanyahu blaming him for compromising Israel's military and urging him to halt the legislation.

The signatories included Ehud Barak, a former Israeli prime minister, and Moshe Yaalon, a former army chief and defense minister. Both are political rivals of Netanyahu.

"The legislation is crushing those things shared by Israeli society, is tearing the people apart, disintegrating the IDF and inflicting fatal blows on Israel's security," the former officials wrote.

"The legislative process violates the social contract that has existed for 75 years between the Israeli government and thousands of reserve officers and soldiers from the land, air, sea and intelligence branches who have volunteered for many years for the reserves to defend the democratic state of Israel, and now announce with a broken heart that they are suspending their volunteer service," the letter said.

Israel Katz, a senior Cabinet minister from Netanyahu's Likud party, said the bill would pass one way or another on Monday.

"I represent citizens who are not ready to have their voice canceled because of threats of refusal to serve" or by those blocking the airport, highways and train stations, he told Channel 12 TV. "There is a clear attempt here to use military service to force the government to change policy."

After seven straight months of the most sustained and intense demonstrations the country has ever seen, the grassroots protest movement has reached a fever pitch.

The parliament is expected to vote Monday on a measure that would limit the Supreme Court's oversight powers by preventing judges from striking down government decisions on the basis that they are "unreasonable."

Proponents say the current "reasonability" standard gives the judges excessive powers over decision making by elected officials. But critics say that removing the standard, which is invoked only in rare cases, would allow the government to pass arbitrary decisions, make improper appointments or firings and open the door to corruption.

Monday's vote would mark the first major piece of legislation to be approved.

The overhaul also calls for other sweeping changes aimed at curbing the powers of the judiciary, from limiting the Supreme Court's ability to challenge parliamentary decisions, to changing the way judges are selected.

Protesters, who make up a wide swath of Israeli society, see the overhaul as a power grab fueled by various personal and political grievances by Netanyahu, who is on trial for corruption charges, and his partners, who want to deepen Israel's control of the occupied West Bank and perpetuate controversial draft exemptions for ultra-Orthodox men.

In a speech Thursday, Netanyahu doubled down on the overhaul and dismissed as absurd the accusations that the plan would destroy Israel's democratic foundations.

"This is an attempt to mislead you over something that has no basis in reality," he said. Alarmed by the growing mass of reservists refusing to serve, the country's defense minister, Yoav Gallant, pushed for a delay in Monday's vote, according to reports in Israeli media. It was unclear if others would join him.

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