France's Chief Rabbi Gilles Bernheim on Thursday joined other religious leaders in opposing the country's plans to authorise gay marriage.
In an open letter to the government and lawmakers, Bernheim, the head of France's Jewish community, said marriage needed to be protected as an institution solely between men and women.
"The argument that marriage is for all of those in love does not hold - it is not because people love each other that they systematically have the right to marry," he said in the letter.
"Marriage is not only a recognition of love. It is the institution that links the joining of a man and woman with the succession of generations."
Government ministers are expected to approve a draft law authorising gay marriage on October 31 despite mounting opposition to the proposed legislation.
Officials have said the legislation will also include provision for married gay couples to adopt children.
More than 1200 French mayors or deputy mayors have signed a petition opposing the government's plans and senior figures in the Catholic Church have voiced fierce opposition.
Pope Benedict XVI last month urged French bishops to oppose the bill and defend marriage as the "foundation of social life".
Cardinal Philippe Barbarin, the archbishop of Lyon, sparked outrage last month when he said legalising same-sex marriage could lead to polygamy and incest.
Opinion polls suggest up to two thirds of French voters back the right of homosexuals to marry but they are evenly split on allowing them to adopt.