Under Amour says such use of "I will" is "likely to cause confusion, mistake, and deception." Under Amour said that it has been using its "I will" phrase on hundreds of products, packaging and various types of marketing since as early as 1998.
In an email response to The Associated Press, Nike spokeswoman Mary Remuzzi declined to comment at this time, saying the company just learned of the lawsuit.
According to the documents, Under Armour is requesting a permanent injunction to bar Nike from using the "I will" phrase. It is also wants Nike to destroy all products, packaging and signs that use the tagline. It also wants Nike to pay Under Armour all profits arising from the use of the phrase, and is seeking to recoup damages.
The suit was filed Thursday in federal court in Baltimore.