Jonathan Lovvorn, a vice president with the Humane Society, said in a statement it was "outrageous and patently illegal" for the government agency to allow the killing of sea lions while at the same time increasing harvest quotas for fishermen.

Salmon-gobbling pinnipeds have been a problem in West Coast waters for over a decade and at the Bonneville Dam for about five years. About 100 California sea lions make the 150-mile (241-kilometre) trip upriver to feast on spawning salmon channelling into the dam's fish ladders.

State and federal governments have spent billions trying to protect once-abundant salmon and fishery managers have also proposed a virtual shutdown of salmon fishing this year in California and Oregon coastal waters.

The Humane Society said killing sea lions is unnecessary since this year's salmon run on the Columbia River is expected to be triple last year's migration, prompting authorities to raise human fishing quotas on the river.

Officials have tried to drive the sea lions away using non-lethal methods such as protective barriers, firecrackers and rubber bullets. The Humane Society has pushed for authorities to continue with these methods.

The suit names the Secretary of Commerce and the National Marine Fisheries Service director as defendants.

Spokesmen for both the federal agency and the Oregon Department of Fish and Wildlife declined to comment, saying they have not had a chance to look at the lawsuit.