Investors are teetering over reports on Friday of Amazon.com Inc.'s (AMZN) interest in creating its own private-label sportswear.

Lululemon Athletica inc. (LULU) , for instance, saw its stock drop nearly 4% to $57.60 between 3:00 p.m. and 3:20 p.m., when the story broke. Shares of Dicks Sporting Goods, Inc. (DKS) also tumbled about 1.5% in the timeframe, while Under Armour Inc. (UAA) dropped 2%. Nike, Inc. (NKE) and Adidas AG (ADDYY) were largely unchanged.

Amazon tapped two Taiwanese suppliers to explore a private-label athletic apparel line, Bloomberg reported. The manufacturers include Makalot Industrial Co., a vendor that produces offerings for Gap Inc. (GPS) and Kohl's Corp.  (KSS) , as well as Eclat Textile Co., which makes products for Nike, Lululemon and Under Armour.

The sportswear line is a new project and long-term contracts have yet to be signed, sources told Bloomberg. The two suppliers will be making a small number of products as a trial run.

Amazon boasts private-label products across dozens of categories, including snacks, electronics, baby wipes, home decor and multiple fashion lines. For some of these products, Amazon is already stealing market share, according to a November 2016 report from data analytics platform 1010data. For instance, it's AmazonBasics brand is responsible for one-third of all online battery sales, seeing 93% year-over-year growth.

It seems that Amazon has also been quietly raking in talent for the sportswear project, hiring Kirsten Harris from Nordstrom Inc.'s (JWN) activewear brand, Zella.

Meanwhile, Nike and Under Armour have not done so well in recent quarters. Nike lowered its sales forecast last month and even offered an unprecedented 40%-off promotion on Groupon, a sign of trouble, analysts said.

Guess this means athleisure is nowhere close to its peak.

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