Judge Hammadi Rahmani said a meeting of judges on Saturday voted unanimously to suspend work in all courts, and to start the sit-in.
Anas Hamaidi, president of the Association of Judges, said the strike begins on Monday in all judicial institutions - and could be extended.
"This injustice will not pass in silence .... These free voices will never be silenced," Hamaidi said. "The attack was not only against judges, but on the law and freedoms."
President Kais Saied this week dismissed 57 judges, accusing them of corruption and protecting terrorists in a crackdown on the judiciary - a move observers say is the latest step to tighten his grip on power.
Among the judges sacked was Youssef Bouzaker, the former head of the Supreme Judicial Council whose members Saied replaced this year.
In a session attended by hundreds of judges, some of the dismissed judges said the purge came after they rejected interventions from the justice minister and in some cases from people surrounding the president.
Last summer, Saied seized executive power in a move his foes called a coup, before setting aside the 2014 constitution to rule by decree and dismissing the elected parliament.
Last summer, Saied seized executive power in a move his foes called a coup, before setting aside the 2014 constitution to rule by decree and dismissing the elected parliament.
Rahed Ghannouhci, the speaker of dissolved parliament called in statement for "national forces, parties, civil society, to stand by the judges in resisting the brutal dictatorship to preserve an independent judiciary".