WASHINGTON — Defense legislation backed by Republicans would inadvertently kill 250 marine mammals and permanently injure 3,000 others, according to House Democrats fighting to keep out “anti-environmental” measures.

It’s the latest flashpoint in a years-long fight—over government protections for the sage grouse and other wildlife—that has centered around the must-pass annual defense policy bill. Though lawmakers hope to wrap up talks to reconcile the House and Senate versions of the 2019 National Defense Authorization Act this month, such debates have caused delays in years past.

On Tuesday, 119 House Democrats sent a letter to leaders of the House, Senate and armed services committees to ask that two provisions be stripped. They did not, however, explicitly threaten to vote against the bill en masse if the language stays in.

“Provisions included in the House bill would undermine the science-based decision-making process used to protect all wildlife, plants, and fish in danger of extinction under the Endangered Species Act,” the letter reads. It was led by House Natural Resources Committee Ranking Member Raul Grijalva, D-Ariz., and House Democratic Whip Steny Hoyer, D-Md.

The lawmakers took issue with House bill provisions that would block the government from listing the sage grouse and the lesser prairie chicken as endangered species for 10 years — and kick the American burying beetle off the endangered species list altogether.

The law requires the military to get government approval from the National Marine Fisheries Service every five years for plans to mitigate activities that may harm whales and other warm-blooded sea creatures. The House-passed bill would extend that to 10, Democrats lamented, adding that “impacts from Navy activities can be significant.”

The estimates of whale and marine mammal deaths and injuries, and foraging disruptions, were based on Navy projections, according to the lawmakers. The Navy has routinely acknowleged the detrimental impact of training and testing — with sonar and explosive ornance — on marine life, though critics have claimed it is not doing enough to mitigate those activities.

In past years, Senate Armed Services Committee Chair John McCain, R-Ariz., SASC Ranking Member Jack Reed, D-R.I., and HASC Ranking Member Adam Smith, D-Wash., have successfully fought to keep the sage grouse issue out of the final bill.

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While House Armed Services Committee Chairman Mac Thornberry, R-Texas, has in the past been beholden to House GOP leaders’ preference for the sage grouse provisions to stay in, he has in recent months said he would oppose anything non-germane to the bill if it threatens passage.