A coalition of environmental groups yesterday accused Canada, Mexico, and the U.S. of holding secret talks that could weaken environmental protection under the North American Free Trade Agreement. The enviros accuse Canada of leading a charge to weaken the Commission for Environmental Cooperation, an environmental watchdog set up under NAFTA to make sure the three trading nations are adequately enforcing their environmental laws. In a letter sent to government ministers, 91 green groups called on the three countries to immediately end their closed-door negotiations, which have apparently gone on for 10 months.