"I urge your administration to take aggressive action ... to insure that imports from China and other countries are free of illegal and dangerous substances," Sen. Evan Bayh, a Democrat from Indiana, wrote in a letter to Bush.

He suggested better coordination between government agencies as one step that might prevent more food safety scares like the one related to melamine, a chemical that surfaced in U.S. pet food supplies earlier this year.

Two food processors in China are suspected of adding the chemical to vegetable proteins used in feed for pets, hogs, poultry and fish. It was also detected in animal feed, but officials insist that presents no real risk to humans.

"We must treat this as a wake-up call to take more aggressive steps to guard against contamination of the food supply," continued Bayh, who also wrote a letter to the head of the U.S. Food and Drug Administration.