The plaintiffs are Center for Biological Diversity, Preserve South Bay, San Diego Audubon Society, Sierra Club and Preserve Wild Santee. The lawsuit accuses the Federal Highway Administration, U.S. Fish and Wildlife Service and U.S. Army Corps of Engineers of improperly issuing permits for the freeway project in violation of several environmental protection laws.

Foes say the construction of the South Bay extension, which would run from state Route 54 in Spring Valley to state Route 905, violates the Federal Endangered Species Act and threatens with extinction at least 10 plants and small organisms.

The project, which has been planned for several years, received its final permit in July from the Army Corps of Engineers. The Federal Highway Administration approved the project last year.