MEXICO CITY (AP) _ The managers of 15 U.S. mutual funds announced Friday they are joining a boycott against Japan's Mitsubishi Co. to protest its plans to build a new salt factory on a Mexican lagoon used by gray whales for birthing.

The area where Mitsubishi operates the world's largest salt evaporation plant in conjunction with the Mexican government _ and where they are planning to build another $150 million plant _ is also Latin America's largest biosphere reserve and the winter refuge of the gray whale.

The whales spend their summers feeding in the Bering Sea and the Gulf of Alaska and swim to the San Ignacio Lagoon on the Baja California peninsula to breed during the winter.

The investors' decision ``sends a wake-up call to Mitsubishi that a whole community of investors thinks that their environmental performance is so bad that they don't want to invest in the company,'' said Jared Blumenfeld of the International Fund for Animal Welfare.

The Mitsubishi boycott is supported by the Calvert Group, Citizens Funds, Crown Futures, Domini Social Investments, Everest Asset Management, First Affirmative Financial Network, Global Environment Fund, Green Century Fund, Miller/Howard Investments, MMA Praxis, Parnassus, Pax World Fund, Prentiss Smith & Co., Trillium Asset Management and Walden Asset Management.

Environmental groups have launched an international campaign to prevent the expansion. In July, 34 distinguished scientists signed an open letter protesting the expansion plans.

The investors' support for IFAW's ``Don't Buy It'' campaign against the company ``will start a movement by other investors to think twice before they invest in Mitsubishi,'' Blumenfeld said.

James Brumm, executive vice president for Mitsubishi International, said the company's plans are compatible with the environment and that the investors backing the campaign did not have all the facts on the proposal.

The saltworks would pump 6,600 gallons out of the lagoon each second and flood more than 115 square miles to create evaporation pools, the scientists said.