Spencer Soper

Bloomberg News

Amazon.com Inc.’s determination to offer shoppers the best deals is prompting merchants selling products on its marketplace to raise their prices on competing websites, a testament to the company’s growing influence over the e-commerce market.

Amazon constantly scans rivals’ prices to see if they’re lower. When it discovers a product is cheaper on, say, Walmart.com, Amazon alerts the company selling the item and then makes the product harder to find and buy on its own marketplace – effectively penalizing the merchant. In many cases, the merchant opts to raise the price on the rival site rather than risk losing sales on Amazon.

Pricing alerts reviewed by Bloomberg show Amazon doesn’t explicitly tell sellers to raise prices on other sites, and the goal may be to push them to lower their prices on Amazon. But in interviews, merchants say they’re so hemmed in by rising costs levied by Amazon and reliant on sales on its marketplace, that they’re more likely to raise their prices elsewhere.

Antitrust experts say the Amazon policy is likely to attract scrutiny from Congress and the Federal Trade Commission, which recently took over jurisdiction of the Seattle-based company. So far, criticism of Amazon’s market power has centered on whether it mines merchants’ sales data to launch competing products and then uses its dominance to make the original product harder to find on its marketplace. Harming consumers by prompting merchants to raise prices on other sites more neatly fits the traditional definition of antitrust behavior in the U.S.

“Monopolization charges are always about business conduct that causes harm in a market,” said Jennifer Rie, an analyst at Bloomberg Intelligence who specializes in antitrust litigation. “It could end up being considered illegal conduct because people who prefer to shop on Walmart end up having to pay a higher price.”

In an emailed statement, an Amazon spokesperson said: “Sellers have full control of their own prices both on and off Amazon, and we help them maximize their sales in our store by providing them insights on how to be the featured offer.” Walmart declined to comment.

Online merchants typically sell their products on multiple websites, including Amazon, EBay Inc. and Walmart Inc., which also removes products with “highly uncompetitive” prices compared with those on other sites. But merchants often generate most of their revenue on Amazon, which now accounts for almost 40% of online sales in the U.S., according to EMarketer.

Merchants have long complained that Amazon wields outsize influence over their businesses. Besides paying higher fees, many now have to buy advertising to stand out on the increasingly cluttered site. Some report giving Amazon 40% or more of each transaction.

Some merchants are keen to increase their sales on Walmart, which charges less to sell products on its marketplace. But sellers say the price alerts are forcing them to maintain allegiance to Amazon and making it harder to diversify their businesses.