The suit argues that despite the long co-existence of the two organizations using the same term for its members and group, the Boy Scouts don’t have the right to use that word by itself when marketing itself to girls.

The suit alleges that confusion among names will “marginalize the Girl Scouts Movement by causing the public to believe that GSUSA’s extraordinarily successful services are not true or official ‘Scouting’ programs, but niche services with limited utility and appeal.”

The Boy Scouts group said in May 2018 that it would change its name for its program for 11 to 17 year olds from Boy Scouts to Scouts BSA when it announced that it would accept girls immediately into its younger Cub Scouts program.

The lawsuit refers to that change, and says that these changes dramatically alter the long-standing relationship of the two groups. The suit mentions a video posted in July that features girls and uses the slogan “Scout Me In.” It also cites and includes several examples of local Boy Scouts chapters using the term “Girl Scouts” by itself and in connection with Boy Scouts.

While it’s impossible to register a trademark in a generic word used in isolation, like scout, trademark law provides protection in narrowly defined areas to provide distinction among competing products—or scouting organizations.

The Boy Scouts of America said in a statement to Fortune that it is reviewing the lawsuit. The statement noted, “We applaud every organization that builds character and leadership in children, including the Girl Scouts of the USA, and believe that there is an opportunity for both organizations to serve girls and boys in our communities.”

The group noted that it has already registered 62,000 girls in the Cub Scouts, which covers ages 7 to 10. It also has 170,000 girls in three other programs it’s run since 1971, including Sea Scouts.

The Girl Scouts of the USA told Fortune that it doesn’t comment on pending litigation. However, the organization added, “The action Girl Scouts took today are in keeping with standard practice in any field, and we did what any brand, company, corporation, or organization would do to protect its intellectual property, the value of its brand in the marketplace, and to defend its good name.”

Cub scouts are organized into small dens and larger packs. The dens must be single gender, but packs can opt to comprise only a single gender or mixed-gender dens. The Boy Scouts said in May that it would expand inclusion of girls in February 2019 to “Scouts BSA,” covering ages 11 to 17, allowing girls to reach the Eagle Scout rank.

The Boy Scouts has seen a plunge in membership, dropped from 2.8 million kids as recently as 2012 to 2.3 million by 2016. That came in part because of reactions from religious and conservative parents and children to the Boy Scouts increasing acceptance of broader sexual identity and orientation, reversing bans on gay troop leaders, and gay and transgender kids.

A move by the Mormon Church to shift its official support away from the Boy Scouts will lead to a further decline. Nearly 200,000 Mormon-affiliated scouts have already left the Boy Scouts, and another 250,000 will move to a new program run by the church by 2020.

The Girl Scouts are also seeing significant declines in membership, off from a peak in youth membership of 2.9 million in 2003 to 1.8 million today.