With the hope to underscore France's environmental credentials ahead of the Copenhagen conference on climate change, President Nicolas Sarkozy plans to make France the biggest economy to impose carbon tax from January 1. The plan, aimed at lowering the energy consumption, was annulled by the Constitutional Court just 48 hours before it was due to come into force on Wednesday.

The Constitutional Court objected that 93 percent of industrial carbon dioxide emissions would be exempt, arguing that the measure would do nothing to combat global warming and unfairly penalize low earners and crowed victory, going against the principal of equality.

The measure announced by Mr Sarkozy in September, in the face of public opposition at a new tax, turned to be controversial and was opposed by the opposition Socialists and the governing UMP party.

François Bayrou, head of the centrist Democratic Movement, criticizing the plan, said that the tax was "a perfect illustration of the methods" of Mr Sarkozy, as it was incomplete and biased. In addition, he added that the party would scratch and oversee an ecological fiscal reform.

François Fillon, Prime Minister, said on Wednesday that changes to satisfy the constitutional council would be presented to the cabinet on January 20. A carbon tax remained a "priority for the President of the Republic and the government", he said in a statement.

The French government has promised to cut greenhouse gas emissions by 75 per cent from 1990 levels by 2050.