The crowd gathered in front of the Supreme Court, carrying Israeli flags banners decrying what the demonstrators view as judicial interference in the government's proposals, an AFP correspondent said.
"We think that the hearing should not even take place because it is not possible for the court judge its own undefined role," said protester Racheli Van Buren, 59.
She called the planned court hearing, scheduled for Tuesday, part of "something illogical".
Judges are due to examine petitions to annul parliament's July vote to limit the so-called "reasonableness clause" used by the nation's top court to review some government decisions.
Critics of the reforms advanced by Prime Minister Benjamin Netanyahu's government fear they could pave the way to more authoritarian rule.
Other proposals include handing the government a greater say in the appointment of judges.
Netanyahu's administration, a coalition between his Likud party and extreme-right and ultra-Orthodox Jewish allies, argues that the legal changes are needed to rebalance powers between lawmakers and the judiciary.
Opponents accuse Netanyahu, who has been fighting corruption charges in court, of conflict of interest.
Since the government unveiled the judicial overhaul plans in January, they have split the nation and sparked one of the biggest protest movement in Israel's history.
Anti-government protests have demonstrated weekly in the commercial hub of Tel Aviv as well as other cities.
Government supporters have also occasionally rallied in favour of the reforms.
