What happened

Shares of Blue Apron Holdings Inc. (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 (AMZN -1.49%) 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.