Back in June 2020, Lululemon entered the booming home gym market in pandemic fashion by acquiring home fitness startup Mirror for $500 million. Now, Nike has filed a lawsuit against the company over Mirror, accusing it of patent infringement. According to CNBC and The Wall Street Journal, Nike’s lawsuit alleges that Mirror – a full-size interactive mirror that brings live fitness instructors to users’ homes – and its app use technology and patents it invented.

The athletic apparel giant specifically cites a patent it filed in 1983 for a device that prompts users to exercise, monitors their heart rate, and determines how fast they are running and how many calories they are burning. Nike also has a number of mobile apps for fitness, including Nike Running Club and Nike Training Club.

Back on November 3, Nike sent Lululemon a list of its allegedly infringing patents. As you might expect, the company, known for producing yoga pants and other types of fitness wear, disagreed with Nike’s assessment. A spokesperson told the publication in a statement that the patents are “overly broad and invalid”. They also said that Lululemon is confident in its position and “looks forward to defending it in court.”

Mirror operates as a separate company within Lululemon, putting the fitness apparel maker in direct competition with the likes of Peloton and Tonal. Lululemon CEO Clavin McDonald previously said the acquisition was about connecting with consumers because the more they deal with the brand the more they deal with, the more they are bound to spend. Last month, however, the company cut its sales forecast for the device in half, calling 2021 “a challenging year for digital fitness.

This isn’t the only patent-related legal battle Lululemon has been involved in. Last year, it filed its own patent infringement lawsuit against Peloton, claiming that the other company’s designs for a new line of leggings and sports bras infringed on its intellectual property.