GoldieBlox reworked the lyrics to the Beastie Boys hit "Girls" for a video advertising their toys, which encourage young girls to pursue engineering and science projects.
The company, founded by a Stanford university alumnus, is now a finalist in a contest to have the commercial air during the 2014 Super Bowl.
GoldieBlox filed a lawsuit pre-emptively, claiming it had the right to use the music because it's a parody. The Beastie Boys responded with the public letter.
"When we tried to simply ask how and why our song "girls" had been used in your ad without our permission, you sued us," the group wrote in the letter.
The Beastie Boys say they support empowering young girls but the group does not permit its music to be used in advertisements.