Dana Mattioli:

Amazon.com Inc. AMZN -1.93% has adjusted its product-search system to more prominently feature listings that are more profitable for the company, said people who worked on the project—a move, contested internally, that could favor Amazon’s own brands.

Late last year, these people said, Amazon optimized the secret algorithm that ranks listings so that instead of showing customers mainly the most-relevant and best-selling listings when they search—as it had for more than a decade—the site also gives a boost to items that are more profitable for the company.

The adjustment, which the world’s biggest online retailer hasn’t publicized, followed a yearslong battle between executives who run Amazon’s retail businesses in Seattle and the company’s search team, dubbed A9, in Palo Alto, Calif., which opposed the move, the people said.

Any tweak to Amazon’s search system has broad implications because the giant’s rankings can make or break a product. The site’s search bar is the most common way for U.S. shoppers to find items online, and most purchases stem from the first page of search results, according to marketing analytics firm Jumpshot.