The Girl Scouts of the United States of America have filed a lawsuit against the Boy Scouts of America for dropping "boy" from the scout group's name.
But the Girl Scouts say the change could erode their brand, calling the move "uniquely damaging" to them.
Their lawsuit seeks damages and an injunction against trademark breaches.
"Only GSUSA has the right to use the Girl Scouts and Scouts trademarks with leadership development services for girls," papers filed in a Manhattan federal court said.
The switch could "marginalise" the Girl Scouts, the complaint reads. It reportedly says the switch has already caused confusion, with some believing their organisation had merged with the Boy Scouts.
In response, the Boy Scouts of America issued a statement saying it was reviewing the suit, and that it believed "there is an opportunity for both organizations to serve girls and boys in our communities".
The Cub Scouts, for ages seven to 10, opened its local clubs to all children in 2018. Boy Scouts, for ages 11 to 17, will follow its footsteps next year when the programme name change becomes official.
The Boy Scouts reportedly have close to 2.3m members in the US, down about a third since 2000, compared with around 2 million members for the Girl Scouts.