On Monday, Chinese and U.S. officials butted heads over whether a contaminated blood thinner caused severe allergic reactions linked to dozens of deaths. On Tuesday, lawmakers will investigate whether U.S. inspectors would have even spotted such contaminants at the source.

The House Energy and Commerce subcommittee is examining how thoroughly the Food and Drug Administration inspects overseas manufacturing plants where nearly 40 percent of the medicines sold in the U.S. are made.

The hearing comes less than a month after FDA revealed that more than 60 people have died of side effects seen with a contaminated batch of the blood thinner heparin that was manufactured in China. Previous estimates pegged the number of deaths at about 20.

The FDA can't say for sure what caused the reactions, but the chief suspect is a contaminant that the agency discovered in supplies of raw heparin coming from China.

However, on Monday Chinese officials raised the possibility that the problems started in the U.S., and said they plan to visit a Baxter International plant in New Jersey to get a better picture of how the finished product is developed. Raw heparin is derived from pig intestines, often processed by small, unregistered workshops in China. The raw ingredient for Baxter's recalled heparin came from Wisconsin-based Scientific Protein Laboratories, which in turn owns a Chinese factory Changzhou SPL and buys additional raw heparin from other Chinese suppliers.

FDA Commissioner Andrew von Eschenbach is expected to highlight the agency's plans to open a new office in China next month during Tuesday's hearing, which begins at 10 a.m. EDT.

Lawmakers will also hear from FDA's science advisers, who recently said the agency needs at least $375 million in new funding next year to repair its understaffed, outdated inspection program.