Whole Foods Market, once a paragon of leisurely high-end shopping, has become a battleground where well-heeled shoppers fight for elbow room and choice salmon cuts with harried delivery couriers.

Since Amazon.com Inc. bought the natural grocer in 2017, Whole Foods stores have been flooded with what the company calls Prime Now shoppers, under pressure to accurately fill grocery orders for customers to arrive in as little as an hour. As these hired shoppers dash through aisles and bang carts into shelves of quinoa, there is less room for the niceties that many customers felt justified the chain’s “whole paycheck” reputation for high prices.

“The folks running around to fill delivery orders is just unpleasant,” said Julie Gelfat, a San Diego resident who recently abandoned her once-beloved Whole Foods for a natural organic local chain called Lazy Acres Market Inc.

Amazon’s push into grocery has upset the applecart for supermarkets across the U.S. Kroger Co. , Albertsons Cos. and others are expanding online shopping and striking deals with delivery companies such as Instacart Inc.

As a result, a legion of gig-economy shoppers has flooded U.S. supermarkets, scouring shelves for goods customers have ordered online. That is causing consternation in aisle three.