Lawmakers voted Thursday to subpoena nine companies responsible for analyzing the most dangerous food entering the country as part of an investigation that gained more urgency with an outbreak of salmonella from tomatoes. For months, a House Energy and Commerce subcommittee has investigated the possible circumvention of government import alerts. Foods posing a potential danger can enter the marketplace only after a laboratory has determined that they are safe, according to Food and Drug Administration rules. But investigators have been told that it is a routine practice for private labs to test food until a clean result is obtained. "This repeated testing is done without FDA knowledge that potentially dangerous food has been imported into this country and has entered commerce," said Rep. Bart Stupak, D-Mich., and chairman of the House subcommittee that authorized the subpoenas. SALMONELLA: Tainted tomatoes make 228 ill RESPONSE: Markets, restaurants pull tomatoes OUTBREAK: Initial wave of sickness strikes 150 Stupak said nine of 10 companies declined to submit information voluntarily out of concern that the food import companies that hire them would then sue them for breaching confidentiality agreements. The records sought related to testing of food found not to meet FDA standards for import into the U.S. After the 10-0 vote to issue the subpoenas, lawmakers heard from an array of witnesses critical of the FDA's strategy for improving food safety. The agency is dealing with a salmonella outbreak that has sickened 228 people in 23 states. Lawmakers said they were frustrated that the agency had yet to identify the source of the contamination and stressed that they were alarmed about yet another outbreak. Citing previous safety issues with spinach, seafood and cantaloupes, they made clear that some blame for the pattern lies with the FDA. "You've had time," said Rep. Marsha Blackburn, R-Tenn. "We're still waiting." The FDA is responsible for ensuring the safety of about 80% of the nation's food supply