The state of California is suing three of the nation's biggest canned tuna companies alleging they failed to warn consumers about excessive mercury in their products. The lawsuit says tests of the companies' albacore and light tuna products found mercury levels that -- by state law -- require warnings to consumers. The lawsuit seeks civil penalties and a halt in sales in California unless the companies post signs in grocery aisles or provide warning labels on their products. The three companies are Tri-Union Seafoods, maker of Chicken of the Sea; Del Monte, maker of Starkist; and Bumble Bee Seafoods, maker of Bumble Bee. The US Tuna Foundation says it will prove in court that its products are safe. According to research excessive exposure to mercury can cause serious health problems, especially in pregnant women and children.