A new study from researchers at MIT’s Center for Energy and Environmental Policy Research has found that the median pre-tax hourly income for Uber and Lyft drivers is just $3.37. The researchers, whose study was earlier reported on by NPR, said that 74% of Uber and Lyft drivers are earning less than the minimum wage and 30% are losing money driving their vehicles for the ride-sharing companies.

The study could prove damaging to Uber and Lyft, which both rely on a steady stream of drivers to operate their services. But if drivers believe that they can’t make enough working as drivers, they might go elsewhere.

Both Uber and Lyft say that their drivers earn a nice living. Uber, for instance, tells drivers they can “earn what you need.” Lyft has a calculator on its driver page, where prospects can input how many hours they’d want to work in a respective city and find out how much the average person there makes. A driver working 40 hours a week in New York City, for example, could expect to make $1,120 per week.

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Still, that doesn’t account for their expenses. And while that might seem like a sizable sum, it’s unclear how much their expenses are cutting into their profits.

The researchers found in their survey of 1,100 drivers that the media driver makes 59 cents per mile they drive. They also incur costs of 30 cents per mile.

In a statement to Fortune, Uber had a sharp rebuttal, saying that the research’s “methodology and findings are deeply flawed.” The company added that it has contacted the paper’s authors to discuss addressing those concerns.

Lyft did not immediately respond to a Fortune request for comment.