Tens of thousands of protesters marched on the main highway into Jerusalem on Saturday evening in a last-ditch show of force aimed at blocking Prime Minister Benjamin Netanyahu's contentious judicial overhaul. More than 100 of Israel's former security chiefs signed a letter pleading with the Israeli premier to halt the legislation. The arrival of the marchers turned the city's main entrance into a sea of blue and white Israeli flags as they completed the last leg of a four-day, 70 kilometer (45-mile) trek from Tel Aviv to Israel's parliament. The marchers joined forces with hundreds of other protesters and planned to camp outside the Knesset, or parliament, ahead of Monday's expected vote. 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. 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. Over 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 defense, undermining the Israeli Defense Forces and urging him to halt the legislation. The signatories included Ehud Barak, a former Israeli prime minister. “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,” they 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. 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 prevent the Supreme Court 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. Protests were also planned on Saturday evening at the central square of the coastal city of Tel Aviv, Israel's main hub. 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. Read More Ukraine war’s heaviest fight rages in east - follow live Charity boss speaks out over ‘traumatic’ encounter with royal aide Fierce protests have been rocking Israel for months. What's fueling them? Thousands march from Tel Aviv to Jerusalem to protest Israeli government's judicial overhaul plan Ex-Israeli security chief backs reservists' protest as Netanyahu allies advance judicial overhaul