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Amazon found itself at the center of a brewing privacy controversy on Tuesday after the American Civil Liberties Union disclosed that the tech giant is selling facial recognition technology to law enforcement that the company has said “helps identify persons of interest against a collection of millions of faces in real-time.”

In a letter to CEO Jeff Bezos, the ACLU and a couple dozen other civil rights organizations called on Amazon to “stop powering a government surveillance infrastructure that poses a grave threat to customers and communities across the country.”

The facial recognition technology, called Rekognition, is sold by the company’s fast-growing Amazon Web Services unit that generated sales of more than $17 billion for Amazon in 2017.

In an AWS blog post from November, Amazon said that the Washington County Sherrif’s Office in Oregon “has been using Amazon Rekognition over the past year to reduce the identification time of reported suspects from 2-3 days down to minutes and had apprehended their first suspect within a week by using their new system.”

But the ACLU argued in the letter to Bezos that the technology “is primed for abuse in the hands of governments.”

“This product poses a grave threat to communities, including people of color and immigrants, and to the trust and respect Amazon has worked to build,” it added.

In a statement to the New York Times, an Amazon spokesperson “stressed that the company offered a general image recognition technology that could automate the process of identifying people, objects and activities” and that “the company required customers to comply with the law and to be responsible when using Amazon Rekognition.”

The revelation comes as concerns over law enforcement’s use of facial recognition technology have intensified amid mass protests in the U.S. in recent years over everything from police brutality to gun control to deportation tactics.

Other entities that have used different features of the Amazon Rekognition technology, according to the AWS blog post, include Pinterest and SmugMug, which use it to identify text within images that users upload to their platforms.

At the same time, the ACLU also pointed to Amazon’s own blog post that says “you can accurately capture demographics and analyze sentiments for all faces in group photos, crowded events, and public places such as airports and department stores” as proof that the technology could be used for mass surveillance.

The controversy could resurface privacy concerns about other advanced technologies from Amazon that the company is commercializing. Amazon’s high-tech convenience store, called Amazon Go, uses hundreds of cameras to help identify which products customers pull off of shelves so they can be charged automatically upon exit. Amazon has said that it does not employ facial recognition in these stores.

Amazon’s Alexa-powered Echo devices have also come under fire recently from security researchers who say they have been able to remotely control Echo devices by embedding commands inaudible to humans into music recordings.

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