Food company Unilever is suing a California company that uses the word 'Mayo' in its sandwich spread name, saying that federal regulators and dictionaries define mayonnaise as a spread that contains eggs. The suit claims false advertising by the company Hampton Creek for labeling its egg-free product 'Just Mayo.' Unilever said the word mayo implies that the product is mayonnaise, and Just Mayo is 'stealing market share from Hellmann's'. However, Hampton Creek said it doesn't mislead consumers because it advertises the absence of eggs as a benefit. According to a market-research firm, Unilever holds the biggest share of the U.S. mayonnaise market, which is estimated to be worth $2 billion annually. That's more than twice the size of the ketchup market. Shares of Unilever are down about 10% over the past 6 months.