The decision by the U.S. FDA to allow U infant formula contaminated with melamine or its byproducts onto store shelves is "seriously flawed" and medically risky, according to scientists at the nonprofit group Consumers Union.

The FDA detected either melamine or its byproduct cyanuric acid separately in several containers of infant formula tested in the fall, but never both together. According to the FDA, the potentially dangerous health effects from the industrial chemicals occur only when both are present.

However, in a letter written to FDA commissioner Andrew C. von Eschenbach and U.S. Department of Health and Human Services Secretary-Designate Tom Daschle, consumer advocates argued that the FDA was assuming parents would never feed their babies more than one type of formula. Two formulas could lead to both chemicals being ingested.

So far, melamine has been implicated in the sickening of nearly 300,000 babies in China. It has killed at least six infants there.