The march organized largely by the "Left Front" party and the Communists comes ahead of the French parliament's debate this week on a European fiscal treaty.

The treaty would set up the European Stability Mechanism bailout fund that European leaders hope will help calm a debt crisis that threatens the euro zone and the global economy.

The main conservative opposition party and most of President Francois Hollande's Socialist Party back the treaty. But it has splintered the French left: Far-left parties, the Greens and some dissident Socialists oppose it.

Austerity has fanned recent violence in places like Spain and Greece.

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