Over the last two years, Amazon has aggressively marketed its facial recognition technology to police departments and federal agencies as a service to help law enforcement identify suspects more quickly. It has done so as another tech giant, Microsoft, has called on Congress to regulate the technology, arguing that it is too risky for companies to oversee on their own.

Now a new study from researchers at the M.I.T. Media Lab has found that Amazon’s system, Rekognition, had much more difficulty in telling the gender of female faces and of darker-skinned faces in photos than similar services from IBM and Microsoft. The results raise questions about potential bias that could hamper Amazon’s drive to popularize the technology.

In the study, published Thursday, Rekognition made no errors in recognizing the gender of lighter-skinned men. But it misclassified women as men 19 percent of the time, the researchers said, and mistook darker-skinned women for men 31 percent of the time. Microsoft’s technology mistook darker-skinned women for men just 1.5 percent of the time.

A study published a year ago found similar problems in the programs built by IBM, Microsoft and Megvii, an artificial intelligence company in China known as Face++. Those results set off an outcry that was amplified when a co-author of the study, Joy Buolamwini, posted YouTube videos showing the technology misclassifying famous African-American women, like Michelle Obama, as men.