Traditional grocers were also already under pressure after Kroger (NYSE: KG), the country’s largest supermarket chain, warned of disappointing earnings.

“This is a shot across the bow,” Sean Lynch, co-head of global equities at the Wells Fargo Investment Institute, told the Wall Street Journal. “The worry is that Amazon is going to impact the market, drive margins down.”

U.S. markets continue to trade within range after withstanding a week with a Federal Reserve interest rate hike, renewed political concerns that could delay the Trump administration’s pro-growth agenda and a pullback in the tech sector.

“The data this week has not been encouraging,” Mariann Montagne, a portfolio manager at Gradient Investments LLC, told Bloomberg. “We need to see consumer spending pick up and more confidence across the board before we can get going again. We’re in a weird limbo, coupled with the the summer doldrums. But if we had great numbers coming out, there would be decisions made.”

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