Nearly 300 environmental and social justice groups are calling on the nation's governors to oppose attempts to amend the Endangered Species Act, trying to head off what appears to be shaping up as a series of attacks against the landmark law.

In a letter sent to the National Governors Association on Thursday, the organizations warned the group against endorsing any rewrite of the act during the governors' annual meeting this weekend.

"In the current political environment," the organizations wrote, "any effort to open up the law would likely weaken, if not cripple, its ability to conserve and recover our nation's most imperiled plants and animals."

The advocacy organizations said they expect an attempt this weekend by the Western Governors Association (WGA) to have the national group join its campaign for reforming the law.

The National Governors Association did not immediately respond to a request for comment.

Last year, the WGA adopted a resolution calling on Congress to amend the Endangered Species Act by setting clear criteria for removing recovered species, increasing regulatory flexibility and expanding the role of state governments. The resolution also said using climate change as a factor for listing species as endangered makes it difficult to create a timeline for recovery or a management plan. It said the act "may not be equipped to address this potential global threat to species and habitat."

Republicans in Congress, led by members from Western states, have said they intend to amend or repeal the law because it does not help species recover fast enough.

The WGA's executive director, Jim Ogsbury, testified last week at a Senate hearing on "modernizing" the act, telling lawmakers that it is "premised on a strong state-federal partnership. Western Governors submit that such cooperation should involve full and authentic partnership between the states and Services with respect to species listing, critical habitat designations, establishment of recovery goals and delisting decisions."

Sen. John Barrasso (R-Wyo.), chairman of the Senate Environment and Public Works Committee, which held the hearing, said the act should be amended to improve recovery rates and de-listings.

But the organizations behind Thursday's letter to governors, including the Center for Biological Diversity and the Humane Society, said those arguments are specious attempts to gut the act. Their letter issues a forceful defense of the law, saying it has prevented the extinction of 99 percent of the species listed. They argue that recoveries take decades, while the law was adopted only 44 years ago. More than 700 species, or nearly half those listed, have been protected for fewer than 20 years, according to the letter.

"It is simply not biologically possible for most species to have recovered yet, but many species are recovering at the pace expected by scientists and conservationists at the state and federal wildlife agencies." It said 11 species recovered last year enough to be de-listed or upgraded from endangered to threatened.

The letter also noted a lawsuit filed by landowners in Utah (who named their group People for the Ethical Treatment of Property Owners) arguing that the act should not apply to creatures that live within only one state. A federal judge agreed with the plaintiffs in 2014, though the federal government appealed the case and is awaiting a decision. If the ruling is upheld, the letter says, it could threaten protections for nearly 1,100 species.

The environmental groups are not the only ones defending the law. Democratic state lawmakers in California announced a series of bills on Thursday that would enable the state to enforce federal environmental statutes, including the Endangered Species Act, under state law. The legislation would direct state regulators to maintain safeguards protecting the state's air, water and endangered species as they stand today, even if Congress and the Trump administration weaken federal oversight.

California is home to at least 301 animals and plants listed as threatened or endangered under the Endangered Species Act. Last year, three sub-species of foxes on the state's Channel Islands were removed from the listafter a recovery, while the Santa Cruz cypress was declared threatened rather than endangered.