What happened

Shares of Blue Apron Holdings Inc. (NYSE:APRN) were sliding today as they gave up some of the gains from last week's rally. Though no direct news was out on the meal-kit service, the stock seemed to fall as Amazon.com (NASDAQ:AMZN) prepared to launch its Prime Day blitz of annual sales and with it parallel sales at Whole Foods Market as the e-commerce giant makes its biggest push yet to drive more business to the organic grocery chain.

As a result, Blue Apron stock was down 4.5% as of 12:16 p.m. EDT, with shares having fallen as much as 9% earlier in the session.

A collection of Blue Apron ingredients in recipe cards

Image source: Blue Apron.

So what

Blue Apron wasn't the only grocery company taking a hit today as SUPERVALU was down 1.4% and Kroger and Sprouts Farmers Market had lost less than 1%. Rival Hello Fresh was off more than 2%.

Blue Apron investors have long feared the tie-up of Amazon and Whole Foods as its IPO price took a dive once the deal was announced last June. During and around Prime Day, Whole Foods is offering deals like a $10 credit for customers who spend $10 at Whole Foods, 10% back when they use the Amazon Prime Rewards Visa card, and discounts on a wide variety of items.

Now what 

Blue Apron shares gained 16% last week in part on rumors of a potential acquisition from Costco, but the stock has been volatile since its debut a year ago. While Prime Day itself may not have a direct effect on Blue Apron, it's further evidence that the company faces ample competition in the meal-kit and larger grocery space, and it's already ceded its leadership in the U.S. market to Hello Fresh, a sign of intensifying competition.

Look for more volatility ahead of Blue Apron's second-quarter earnings report, due out Aug. 2.

John Mackey, CEO of Whole Foods Market, an Amazon subsidiary, is a member of The Motley Fool's board of directors. Jeremy Bowman owns shares of Kroger. The Motley Fool owns shares of and recommends Amazon. The Motley Fool has a disclosure policy.