More than a dozen state attorneys general are asking Pres. Donald Trump to throw out recent federal rules regulating the environment for endangered or threatened plants and animals. The states claim the rules, which enlarge the definition of species habitat, give the federal government excessive power over state and private lands.

The rules govern implementation of the Endangered Species Act (ESA), and were made a year ago by Pres. Barack Obama’s administration. In January the state officials sent a letter to the Trump transition team asking for repeal, arguing the rules will cost states and private land owners billions of dollars by blocking or delaying the use or development of their properties. “It’s such a massive land grab by the federal government,” Arkansas Attorney General Leslie Rutledge says. But at least one study shows implementation of the ESA has affected very few development projects during the current decade.

Rutledge, along with Alabama Attorney General Luther Strange (who has since been appointed to the U.S. Senate) spearheaded the letter. Their states and others also filed a lawsuit in U.S. District Court for the Southern District of Alabama in November challenging the new rules. Those rules state, essentially, that agencies determining areas critical to the survival of an endangered species should consider two types of land: One is land currently occupied by that species; the other comprises nearby but unoccupied areas that contain resources, like food or shelter, critical to the species’s survival, or could become so if the species shifts its range.

The attorneys general want the rules rolled back to language used since 1984. At that time, they claim, the rules stipulated that after listing a species as endangered or threatened, federal agencies designate critical habitat only in areas where the species is found at that moment. The attorneys say the rollback would protect private property owners from the uncertainty of having their land declared critical habitat if agencies believe the land may at some point in the future be needed for the species recovery.

The U.S. Fish and Wildlife Service and the National Oceanic and Atmospheric Administration’s National Marine Fisheries Service, along with environmental scientists, say considering both types of land together is important both because the range of an endangered species can change, and nature and human development can sever previously occupied patches of habitat. For instance, a 2016 report from the Ecological Society of America (pdf) noted a large-scale study of climate change on amphibians, birds and mammals showed about half had shifted their ranges to higher latitudes or elevation and about two thirds had shifted toward earlier spring breeding or migration. The same report found that in the U.S. a common threat to listed species is “habitat fragmentation” when land is cleared for farming or economic development, restricting the movement of species and leaving them in isolated spots.

At the same time, regulatory actions had little effect on development, according to a 2015 study. The research, published in the Proceedings of the National Academy of Sciences, found no projects were stopped (pdf) or extensively modified as a result of the 88,290 consultations conducted with the Fish and Wildlife from January 2008 through April 2015. Dan Ashe, former director of the service under Obama, downplays the impact critical habitat designations have on land owners. The designation, he says, does not allow the government to take or manage private property but simply requires that actions “authorized, funded or carried out by federal agencies” must not destroy or adversely modify designated critical habitat.

The state attorneys general, however, point to economic impact statements accompanying critical habitat designations that predict major costs associated with the loss of grazing and timber harvesting, along with oil and gas production and mining on the 625 million acres of federal land in 12 western states including Alaska. For example, estimates from the U.S. Bureau of Land Management in 2013 put economic losses for establishing sage grouse habitat at between $839 million to $5.6 billion annually as well as a loss of between 5,570 and 31,055 jobs, according to a Western Energy Alliance report (pdf).

The bird, whose habitat covers about 165 million acres in the West, ultimately was not listed as endangered or threatened after federal, state and private interests agreed to a national planning strategy that provided stronger protection for 35 million acres of the most important habitats on federal lands.

In the U.S. there are 1,652 plants and animals—from ferns to frogs—listed as endangered or threatened. Critical habitat had been designated for 704 of the species as of January 2015, before the new definitions were made final. The largest proposed area is for Arctic ringed seals, which would protect more than 226 million acres in Alaska’s Bering, Chukchi and Beaufort seas—an area more than twice the size of California.

Arkansas’s Rutledge expects to reach receptive ears in the Trump White House, because the president campaigned on repealing federal regulations whose public good is outweighed by harm to industry and jobs. White House spokeswoman Kelly Love says the administration has indeed ordered agencies to set up task forces to review regulations with an eye on simplifying or eliminating them. But Love says the White House does not yet have enough information to take a position on the critical habitat rule.

Advocates for protecting endangered species do anticipate the new administration—as well as a Republican-controlled Congress—will be hostile to the expanded habitat definitions. “It’s still early but we are gearing up for a long difficult fight,” says Brett Hartl, government affairs director at a nonprofit conservation group, the Center for Biological Diversity. Federal agencies will be more passive than in the past, he believes. “Given the new climate politically, it is unlikely we will see Fish and Wildlife take the initiative but are likely to sit on their hands more.”