French Jewish leaders called for a voters to block the rise of the far-right Front National party, which topped polls in six of the country's 13 regions in the first round of regional elections.
The party is experiencing a surge in the polls following the 13 November terror attacks in Paris, and looks set to take control of at least two regions in the second round of voting on December 13.
The Representative Council of Jewish Institutions in France (CRIF) called on voters to stop the "populist and xenophobic party", warning "not to let the Republic give way in the face of threats".
France's chief rabbi Haim Korsia called for a "civic uprising" of voters in the second round "to breathe life into democracy... in these particularly troubled times for the nation".
The party has attempted to distance itself from its anti-Semitic roots in recent years, with the founder of the party Jean Marie Le Pen expelled for describing the Holocaust as a "detail" of history, and defending war time collaborator Philippe Petain.
Under his daughter, Marine Le Pen, the party has recast itself as an anti-EU organisation and anti-Islam organisation.