DARIEN — An animal rights organization has filed a lawsuit against the federal Fish and Wildlife Service over a new rule requiring references to hunting in the design submissions for its traditional duck stamp contest.

Duck stamps are a $25 license to hunt waterfowl with origins dating back to the Great Depression. Under federal laws, anyone over the age of 16 who wants to hunt waterfowl must purchase a stamp.

Most of that money goes toward conservation efforts for the birds, and as a result, the stamps have also become popular with birdwatchers and other non-hunters.

Each year, the Fish and Wildlife Service holds a national contest for the stamp’s design.

The contest dates back to the Duck Stamp Act’s father, Jay Norwood "Ding" Darling, a Pulitzer-winning cartoonist who drew the first duck stamp in the mid-1930s.

But in May, the agency announced a new rule that artwork submitted to the contest must include hunting imagery.

That rule is at the crux of a lawsuit filed in federal court Tuesday by Friends of Animals, a Darien-based animal rights organization.

“It’s almost comical the desperate lengths the dwindling hunting industry is willing to go to make its clients feel relevant,” Priscilla Feral, president of Friends of Animals, said in a press release. “But jeopardizing crucial wetland habitat protection is not a laughing matter, so we had to take legal action.”

She called the move “anti-wildlife” and “anti-conservation.”

The organization’s suit claims the new rule will “alienate” large swaths of stamp buyers who don’t hunt, including birders and wildlife photographer, according to a draft copy of the complaint the organization provided to Hearst Connecticut Media.

The suit names Interior Secretary David Bernhardt and Fish and Wildlife Service Director Aurelia Skipworth as defendents.

“In issuing the new rule, defendants abruptly changed previous contest regulations that never contained a permanent, mandatory theme of any type for all contest entries,” the complaint alleges.

The suit asks the courts to vacate the contest rule and pay for attorney fees and legal costs.

On Saturday, the Fish and Wildlife Service announced the contest to design the 2021-22 duck stamp had been awarded to an artist in Milford, Delaware.

Friends of Animals have filed similar lawsuits against federal agencies.

Earlier this month, the organization sued Commerce Secretary Wilbur Ross over Mystic Aquarium’s plan to import five Beluga whales from Canada.