The Girl Scouts of the United States of America (GSUSA) have filed a trademark infringement lawsuit against the Boy Scouts of America, after the Boy Scouts decided to drop "Boy" from its namesake program and start welcoming older girls.

Key points: Girl Scouts say name change threatens to "marginalise" Girl Scouts activities

Girl Scouts say name change threatens to "marginalise" Girl Scouts activities Boy Scouts said in May it would make girls eligible to earn highest rank Eagle Scout

Boy Scouts said in May it would make girls eligible to earn highest rank Eagle Scout Girl Scouts said it was looking to "defend its good name"

The lawsuit in Manhattan Federal Court is an attempt by the Girl Scouts, founded in 1912, to avert an erosion of its brand and membership as the Boy Scouts, founded two years earlier, tries to reverse its own decades-long membership decline.

It was filed after the Boy Scouts, which accepts children 11 to 17 years old, said in May it would change its name to Scouts BSA in February 2019, and make girls eligible to earn its highest rank, Eagle Scout.

The Boy Scouts said in a statement it was reviewing the lawsuit.

"We applaud every organisation that builds character and leadership in children, including the Girl Scouts of the USA, and believe that there is an opportunity for both organisations to serve girls and boys in our communities," it said.

Based in Irving, Texas, the Boy Scouts recently had about 2.28 million members, less than half its 1970s peak, while the Girl Scouts, based in Manhattan, said it had about 2 million.

In the complaint, the Girl Scouts said the Boy Scouts had no monopoly over such terms as "scouts" and "scouting" when it offers services to girls.

Girls have been featured prominently in recent Boys Scouts of America ad campaigns. ( Facebook: Boy Scouts of America )

It also said the name change threatened to "marginalise" Girl Scouts activities and had already sown confusion, with families, schools and communities nationwide being told the organisation no longer existed, or had merged with the Boy Scouts.

"Only GSUSA has the right to use the Girl Scouts and Scouts trademarks with leadership development services for girls," the complaint said, adding that the Boy Scouts' infringements were, "new and uniquely damaging to GSUSA".

"We did what any brand, company, corporation, or organisation would do to protect its intellectual property, the value of its brand in the marketplace, and to defend its good name," the Girl Scouts said in a statement.

The Boy Scouts has said its rebranding was part of a single-name approach it adopted when it decided in October 2017 to let girls enrol in the Cub Scouts, for children 7 to 10 years old.

It has also launched a "Scout Me In" campaign, featuring boys and girls.

Reuters