The leader of France's far-right National Front has said she will organise a campaign against the European treaty that would enact strict and enforceable budget rules.
Marine Le Pen told BFM TV that her party's two parliamentarians would vote against the treaty and that the party will organise a campaign opposing it.
Ms Le Pen, who advocates abandoning the euro currency, told the station: "The euro was an error. It's time to fix it."
The French parliament will vote on the treaty in the autumn.
President Francois Hollande's Socialist Party supports the treaty and has a strong majority in the legislature, but members of the party's left wing have expressed opposition.