On Wednesday, the U.S. Fish and Wildlife Service finalized a recovery plan for the Mexican gray wolf that wildlife advocates believe could spell disaster for one of North America’s most imperiled mammals.

Various environmental advocacy groups, including the Sierra Club’s Grand Canyon Chapter, immediately blasted the Trump administration’s plan following its release, arguing that it is insufficient to protect the endangered subspecies. “If it gets implemented, it’s very likely to result in the extinction of the Mexican wolf,” said Michael Robinson, a conservation advocate at the Center for Biological Diversity.

The Mexican gray wolf—a subspecies of the North American gray wolf—was rescued from the brink of extinction following its listing under the Endangered Species Act in 1976. Today the wolves exist in the wild in two distinct, heavily managed “experimental populations”—one in northern Mexico numbering around 31 wolves and one in the southwestern United States numbering around 113 animals. The USFWS plan establishes the boundaries of those populations and contains goals and procedures for the recovery of the subspecies.

“The Fish and Wildlife service is responsible for these highly endangered animals,” said Sandy Bahr, director of the Grand Canyon Chapter. “The recovery plan falls short of what’s needed and far short of what scientists have recommended.”

In 2011, the USFWS enlisted a team of independent scientists to draft a recovery plan for the Mexican gray wolf. That team recommended expanding the United States Mexican gray wolf population to three connected zones with 250 wolves each (a total of 750 animals), warning that small and isolated populations are vulnerable to collapse. The plan released on Wednesday calls for just one United States population of 320 wolves.

The finalized plan restricts the range of that U.S. population to southern Arizona and New Mexico. In their 2011 proposal, the wildlife biologists identified northern New Mexico and the Grand Canyon area as vital habitats for Mexican gray wolf recovery. Since they were reintroduced into the wild in 1998, the wolves have been precluded from those areas, which the scientists said has limited their recovery. The finalized plan maintains the northern boundary of I-40, denying the animal huge swaths of its historical habitat. “I’m particularly disappointed that they continue to limit the recovery area,” Bahr said. “The greater Grand Canyon area has been one of the places identified as very much suitable for recovery.”

The finalized plan is a watershed moment in the long-standing battle over Mexican gray wolf recovery. For decades, wolf opponents—including livestock owners and officials from Arizona and New Mexico’s Game and Fish departments—have lobbied relentlessly against the restoration of Mexican gray wolf populations, stalling the development of a robust recovery plan. On Wednesday, environmentalists lamented that the finalized plan submitted to their influence at the expense of the endangered animal. “The Fish and Wildlife Service has once again sided with the livestock owners who want to destroy the wolves,” said Robinson.

A coalition of environmental groups, including Earthjustice, sent a notice to the USFWS on Wednesday, saying that they intend to fight the plan with a lawsuit.

“It’s never been easy,” said Bahr. “It took challenges and litigation to get wolves reintroduced, and took challenges and litigation to get the Fish and Wildlife Service to take responsibility to recover the wolves. We plan to continue to push for real recovery.”