Thousands of scientists have signed two letters opposing changes to the Endangered Species Act proposed by the Trump administration that critics say would weaken protections in favor of developers, Reuters reported Monday.

The proposed changes were announced by the Interior and Commerce Departments in July, and include axing the "blanket rule' granting threatened species the same protections as endangered species and removing language telling officials not to consider economic impacts when listing a species.

"If enacted, these rules will be an absolute disaster for efforts to save species from extinction," said Dr. Stuart Pimm, Doris Duke professor of conservation ecology at Duke University in a Center for Biological Diversity press release announcing one of the letters. "With humanity's footprint ever growing and climate change looming, we need the Endangered Species Act more than ever. These rule changes are 180 degrees in the wrong direction."

Pimm was one of 273 conservation scientists to sign a letter Monday addressed to Commerce Secretary Wilbur Ross and Interior Secretary Ryan Zinke critiquing three proposed changes: the removal of the "blanket rule," the permitting of economic considerations when deciding whether to protecting species, and changes making it harder to preserve critical habitat for vulnerable species.

The scientists opposed a new definition of "adverse modification" to "critical habitat" that would limit the definition to "alteration that appreciably diminishes the value of critical habitat as a whole for the conservation of a listed species."

"The definition will allow activities to destroy or modify critical habitat so long as they don't affect 'the whole' of critical habitat, which particularly for species with large ranges will allow most if not all destructive actions to move forward," the scientists wrote.

Habitat destruction is the leading cause of harm to endangered species, the scientists said.

They also opposed a rule that would not designate critical habitat for species if the leading cause of threat is climate change, disease or another factor not directly related to habitat destruction.

"Species facing such intractable threats as climate change or disease, need habitat protection to ensure that those places where they are managing to survive in the face of threats are not destroyed and to provide habitat for species migration in response to climate change driven habitat changes," they wrote.

The 273 conservation scientists were joined in their efforts by three agencies representing 9,000 biologists, who sent a separate letter to Zinke and Ross Monday opposing the changes, Reuters reported.

The letters come as the 60-day public comment period on the proposed changes concluded, Reuters said.