The lawsuit against the USDA's Wildlife Services agency came two months after a U.S. judge in neighboring Washington state ruled that the federal agency's environmental assessment of its work was inadequate, and blocked wolf kills in the state.
"The environmental analysis they put out for both Washington and Oregon were virtually identical, which is part of the reason we don't think they did a meaningful analysis in Oregon," said Nick Cady, legal director of Cascadia Wildlands, one of five groups suing to block the wolf-culling program.
The same conservation groups sued in the Washington state case.
Gray wolves, native to Oregon but wiped out in the state by an eradication campaign in the early 20th century, returned in 2008 and have now spread out to multiple parts of Oregon.
Wolves killed at least 30 sheep and cows in Oregon in 2014, according to state figures, and ranchers and hunters have been lobbying for more freedom to kill the predators in a long-standing feud over the level of protections for the carnivorous canids.
In Oregon, animal welfare advocates say Wildlife Services has not shown it is necessary to kill wolves instead of using non-lethal control methods, according to the complaint filed in a U.S. court in Oregon.
Wildlife Services officials did not immediately respond to a request to comment. They previously said agency policy prohibited them from discussing pending litigation. On its website, the agency says it provides "federal leadership and expertise to resolve wildlife conflicts to allow people and wildlife to coexist."
There is no imminent plan for the agency to kill wolves, 81 of which roam the Oregon wilds in 16 packs, Cady said. In 2012, Wildlife Services was chosen as the wolf-killing agency for Oregon. It has not killed any wolves since then, as the state has not asked it to do so.
Wildlife officials last year removed all wolves from state endangered species protections except for a portion on the west side of the state that are still protected under the U.S. Endangered Species Act - and therefore would not be targeted.
(Reporting by Courtney Sherwood in Portland, Ore.; Editing by Eric M. Johnson and Peter Cooney)