At issue is a longstanding definition of “harm” in the Endangered Species Act, which has included altering or destroying the places those species live. Habitat destruction is the biggest cause of extinction, said Noah Greenwald, endangered species director at the Center for Biological Diversity.

The U.S. Fish and Wildlife Service and National Marine Fisheries Service said in a proposed rule issued Wednesday that habitat modification should not be considered harm because it’s not the same as intentionally targeting a species, called “take.” Environmentalists argue that the definition of “take,” though, has always included actions that harm species, and the definition of “harm” has been upheld by the Supreme Court.