"MaCurdy found that the costs of raising the wage are passed on to consumers in the form of higher prices. Minimum-wage workers often work at places that disproportionately serve people down the income scale. So raising the minimum wage is like a regressive consumption tax paid for by the poor to subsidize the wages of workers who are often middle class."
In other words, what people buy the largest percentage of their total purchases from places like Walmart? Raising prices at companies that primarily hire at the minimum wage will increase prices disproportionally for many more poor people, both for minimum wage earners as well as people barely above that wage but still below the poverty line.