For the third time in four years, the scientists oppose a Senate bill that would allow federally recognized tribes to claim ancient remains even if they can't prove a link to a current tribe.
Supporters call such concerns overblown.
They say the changes are intended to clarify the Native American Graves Protection and Repatriation Act, or NAGPRA, to ensure that federally recognized tribes can safeguard the graves of their ancestors.
Neither the Senate bill nor the draft regulations would affect the 9,300-year-old bones known as Kennewick Man, they said. The skeleton was discovered in 1996 along the Columbia River near Kennewick, Wash., and has been the focus of a bitter fight ever since.
A federal appeals court ruled in 2004 that scientists can study the ancient bones, and teams of anthropologists and other analysts have begun poring over more than 300 bones and bone fragments at the Burke Museum of Natural History and Culture in Seattle, where the remains are housed.