When Reich analyzed the adjectives in the Yelp reviews used to describe stores, however, he noticed another telling pattern: Much of the ratings’ language seemed to be about store characteristics, rather than anything to do with race.

In Walmart stores in predominantly black zip codes, customers were more likely to use words like “worst,” “unorganized,” “nasty,” and “slow” to describe their shopping experiences. In predominantly white zip codes, customers used words like “smaller,” “friendly,” and “clean” to review their stores.

Reich says this evidence, along with interviews his team collected from 89 Walmart workers in Los Angeles, Dallas, Chicago, Cincinnati, and Florida, suggest that Walmart systematically understaffs stores in communities of color, a practice he calls “consumer redlining.”

Walmart did not respond to my inquiry about Reich’s hypothesis, but it did issue a statement to Business Insider, saying that it thought Reich’s study was “flawed and without merit.” A spokesperson told the publication, “Our associates play a critical role in the company's success and that's why we've invested $2.7 billion on associate education, training, and wages. We're also proud to provide communities across the country, regardless of social or economic background, access to affordable goods and career opportunities to help them better provide for their families."

At any rate, this perceived understaffing may not be a result of explicit racial animus so much as a natural consequence of Walmart’s business model, which relies on far lower labor costs than its competitors. Since Walmart opens up many stores in areas where consumers already have few shopping options, the chain, Reich argues, has little incentive to invest in labor for these stores, which are often in communities of color.

“When Walmart moves into the South Side of Chicago, it’s not really displacing numerous other businesses,” says Reich. “So it can short-change investments in staff, and force people to work harder. Consumers don’t have a choice about where they’re shopping.”

Anthony Roberts, an assistant professor of sociology at California State University who has written extensively on Walmart’s urban-expansion attempts in recent years, points out that such staffing decisions are integral to Walmart’s model.

“The company utilizes data from its stores to predict the optimal staffing levels at the local and regional levels. Employee compensation is an important factor in this analysis, because the company's retail model depends on low wages for profitability,” said Roberts, in an email. “Given the dependence of these communities on Walmart stores, there seems to be very little need to address poor customer satisfaction.”