A House subcommittee Thursday voted to subpoena the records of nine private laboratories involved in food testing as part of a congressional investigation into allegations that some food companies have withheld information on tainted food from federal regulators.

The subcommittee in May asked 10 labs for records dating back to 2002, but just one, in Miami, complied. The other labs, according to the subcommittee, refused to turn over records, arguing that the documents belong to their clients, food importing companies.

The subpoena vote by the House Subcommittee on Oversight and Investigations occurred in the wake of the Food and Drug Administration's warnings this month about the latest food contamination case: tomatoes tainted with salmonella bacteria. The FDA told consumers in New Mexico and Texas on June 3 to not eat certain types of tomatoes. Four days later the warning was expanded, and grocery chains stopped selling certain types of tomatoes and some restaurants removed them from their menus.

The FDA says that since mid-April, there have been 228 reported cases of salmonellosis nationwide caused by Salmonella Saintpaul, an uncommon form of salmonella and at least 23 victims have been hospitalized.

The FDA's assistant commissioner for food protection, David Acheson, told the subcommittee Thursday that agency scientists are still working to determine where the tomato contamination originated.

During the hearing, subcommittee members asked Acheson why the FDA can't "trace-back" the bad tomatoes and the sources of other food contamination cases. Acheson said the agency is working to acquire that ability.

One problem, he said, "is related to the complexities of a trace-back, where not every tomato has a code on it."

In the wake of the salmonella outbreak, subcommittee members also raised doubts about the food protection plan the FDA unveiled last year.

A Government Accountability Office review of the plan found that the FDA had identified areas of food safety concern, but has not taken steps to activate the plan.

Lisa Shames, the GAO's director of Natural Resources and Environment, said her agency was concerned about the FDA's "lack of specificity on the necessary resources and strategies to fully implement the plan."

Shames noted that her agency raised doubts about the FDA's ability to enforce food safety in 1998.

"A decade later," she said, "the story remains the same and has only taken on a greater sense of urgency."

Shames said that GAO has made 21 recommendations to the FDA regarding food safety since 2004, but that only three have been adopted.

The Bush administration allocated $620 million for food protection programs in 2008, according to the GAO. About $42 million of that amount went to the new food protection plan.

Earlier this week, the administration asked Congress for an additional $275 million for food safety.

Rep. Bart Stupak, D-Mich., the subcommittee chairman, asked Acheson how much the agency's proposed food protection plan would cost over five years.

Acheson said that he could provide plan milestones, but that funding information for five years would prove difficult to estimate.