Cincinnati-based grocery chain owner Kroger Co. (KR) has seen its shares sink more than 18% on Thursday afternoon after management announced a reduction in its full-year earnings guidance. The decline represents KR’s largest dip in more than 15 years, as investors fear pricing wars from American megaretailers and new European incumbents.

Before the opening bell, the nation’s largest operator of traditional supermarkets posted revenues above the consensus estimate while earnings came in line with forecasts. Kroger reported first-quarter adjusted earnings of $0.58 per share on sales up 4.9% year-over-year (YOY) to $36.29 billion. Same-store sales declined for the second consecutive quarter, dipping 0.2% excluding fuel. Over the same period last year, Kroger posted a 2.4% rise. Full-year EPS guidance was trimmed to $2.00 to $2.05, down from the prior estimate of $2.21 to $2.25 and well below the Street’s forecast for $2.22.

Growing Influence of Online Shopping

Investors are particularly sensitive to the disappointing news as Kroger and its U.S. peers face competitive pressure from the entrance of new low-cost German grocers into the American market. At the same time, price cuts from Wal-Mart Stores Inc. (WMT) and a consumer shift to online shopping for produce, led by industry leader Amazon.com Inc. (AMZN), threatens the grocery store operator’s long-term viability.

While Chief Executive Rodney McMullen vowed, “we will not lose on price,” lower prices did cut into profit margins, as gross margins fell to 22.1% of sales from 23% in Q1 of 2016. (See also: Amazon Launches Online Grocery Pickup Service.)

Other U.S. food industry stocks including SuperValu Inc. (SVU), Whole Foods Market Inc. (WFM) and Wal-Mart have taken a hit on Thursday, trading down 5.9%, 6.8% and 1.2% respectively. At $24.77 on Thursday, Kroger’s shares reflect a 29.6% loss in the most recent 12-month period and a 28.2% decline year-to-date (YTD). (See also: US Grocer Kroger Scrambles Before German Invasion.)

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