"The proposal that we have before us is not compatible with the mandate, and the technical analysis that we are carrying out with our EU partners will show this," French Farm Minister Dominique Bussereau told the French Senate.
The European Commission announced the offer last week to cut farm tariffs further in a bid to keep the struggling Doha Round of talks alive at the World Trade Organisation (WTO).
The EU offer would nearly halve its average tariff on agricultural imports to just over 12 percent. The United States and Brazil said the proposal fell short of what was needed.
It came after a warning from French President Jacques Chirac that Paris could torpedo any WTO agreement if it felt it called the EU's Common Agricultural Policy (CAP) into question.
"This respect of the CAP is an absolute red line," Bussereau told the Senate. "If this line were to be crossed, France would use its veto on a potential global accord," he added.
The European Commission immediately rejected the French criticism, saying its latest offer was within its mandate.
"We continue to firmly believe that our offer is within the mandate given to us by the EU Council of ministers," a spokesman for EU Trade Commissioner Peter Mandelson said by telephone.
France is by far the EU's biggest agricultural producer and the main beneficiary of its subsidy and tariff system.