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Amazon's facial recognition tech is again under fire. AI experts on Wednesday drew attention to a movement calling for Amazon to stop selling its facial recognition software, dubbed Rekognition, to law enforcement.

So far, 27 researchers have signed an open letter, published March 26, criticizing Amazon for overlooking other researchers' studies into its Rekognition software. The group is also demanding that Amazon halt sales of the software to police.

The signers included scientists from universities, Google and Facebook, as well as AI scientists like Yoshua Bengio, a winner this year of the prestigious Turing Award.

"We hope that the company will instead thoroughly examine all of its products and question whether they should currently be used by police," wrote the researchers in the letter. "We call on Amazon to stop selling Rekognition to law enforcement as such legislation and safeguards are not in place."

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The open letter came after Amazon's Matthew Wood and Michael Punke wrote several blog posts "attempting to refute the results" of a study conducted by Inioluwa Deborah Raji and Joy Buolamwini, according to the letter. The earlier study said Amazon's Rekognition program has much higher error rates when it's trying to recognize the gender of darker skinned women than lighter skinned man.

Amazon didn't immediately respond to a request for comment.

The American Civil Liberties Union also released a statement supporting the researchers.

"Face surveillance gives governments unprecedented power to track, control, and harm all people, but especially communities of color, immigrants, religious minorities, and others long subject to surveillance abuse," said Matt Cagle, attorney at the ACLU, said in an emailed statement. "Companies seeking to profit off this menacing technology cannot ignore and outsource responsibility for the harms of systems they build. They must stop selling face surveillance to governments entirely."

Since the ACLU called Amazon out for selling Rekognition to law enforcement last June, the company has been under fire over its facial recognition technology. The e-commerce giant's shareholders in January demanded the company to stop selling the program to government agencies.