Montana-based conservation organizations Alliance for the Wild Rockies and Friends of the Wild Swan announced Wednesday they intend to sue the U.S. Fish and Wildlife Service over a bull trout recovery plan released last week.

The plan seeks to establish a framework for conservation of bull trout, which have been listed as threatened under the Endangered Species Act in the Lower 48 states since 1999.

Since the draft plan was introduced, however, it has come under fire from environmental organizations that believe it does too little to protect the struggling fish species.

Michael Garrity, executive director of Alliance for the Wild Rockies, has called it an “extinction plan,” referring to language that would allow for the disappearance of up to 25 percent of distinct bull trout populations identified in four of the six recovery units.

A notice of intent to file suit was sent to Department of the Interior Secretary Sally Jewell on Wednesday. In it, the organizations contend that the plan violates several provisions of the Endangered Species Act and refer to six previous lawsuits filed against the agency over bull trout protections.

“The [Fish and Wildlife] Service has lost every single legal determination it made regarding bull trout over the last 21 years,” the notice states. “We implore you to not make yet another mistake with this recovery plan.”

Contending that the plan violates provisions of the Endangered Species Act, the plaintiffs must give the agency 60 days to correct the alleged violations, after which they may officially file suit.