This is the first time Prime Minister Benjamin Netanyahu's government has flouted a Supreme Court ruling, although it has clashed with the judiciary in the past.
After elections in 2022, it sought to limit the court's powers, drawing global criticism and mass protests in Israel.
The judicial reform was shelved after the October 7, 2023, Hamas attacks although some parts have since been resurrected.
Israeli law requires the Second Authority for Television and Radio to have a minimum number of members to make decisions.
The government argues that because the council no longer meets that requirement, it has no authority to approve appointments or take other actions.
However, on June 17, the court ordered the council to continue anyway.
The cabinet on Sunday voted unanimously in favour of rejecting the court's ruling, Communications Minister Shlomo Karhi and Justice Minister Yariv Levin said in a statement.
The decision was swiftly condemned by opposition leaders vying to replace Netanyahu's coalition in an upcoming election.
Israeli opposition leader Yair Lapid said "the government had turned criminal".
"This is the most serious constitutional crisis in Israel's history. It's the destruction of the foundations of our democracy," he said in a statement.
Karhi and Levin - a key proponent of judicial changes - proposed that the government not recognise any council decisions or actions until the legal threshold for membership was met.
In its vote, the cabinet said the court had no authority to trample on the law and it will "act through all legal means at its disposal to nullify the decision".
"A ruling that contradicts the law will not be recognised and decisions made under it are null and void," it said.
Karhi criticised the court, saying judges are not parliament.
He said any decisions the media regulator makes in the future would be "worthless".
Levin added that when parliament enacts a law, the court must abide by it.
Israeli President Isaac Herzog said that statements of disobedience to Supreme Court rulings harm the core of unity in the country.
"I have already made it clear, and I will repeat it again and again - disobedience to a court ruling is a red line that must not be crossed under any circumstances," he said.
Cabinet Secretary Yossi Fuchs downplayed the ministers' rhetoric, saying there was no call for disobeying the court's decision but rather a "sharp criticism" of a ruling that contradicts the government's law.
"The government declared that it will use all legal tools at its disposal to overturn the decision in the future. How do legal tools become disobedience to a ruling?" Fuchs wrote in an X post.
Netanyahu has not commented on the cabinet's decision but his rivals did, while legal experts expressed worries of a constitutional crisis.
"Not adhering to court rulings brings anarchy in the streets and the disintegration of our country," said Naftali Bennett, who was prime minister from 2021 to 2022.
Similarly, Gadi Eisenkot, who is leading in polls to replace Netanyahu, said Israel's government was "raising a hand against Israeli democracy" and that Netanyahu was "dividing Israel".
The cabinet's decision could affect the possible approval of the sale of Israel's Channel 13, one of the country's major commercial television networks and a critic of Netanyahu, to a group of high-tech entrepreneurs.
It may also affect whether the pro-Netanyahu Channel 14 should continue to be classified as a "small channel" - a designation that grants it regulatory benefits and exemptions.
A date for new elections has not yet been set but one is expected in September or October.
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