Facebook said on Wednesday that it may have “unintentionally uploaded” the email contacts of around 1.5 million users, a report from Reuters says. The uploads may have been going on since May 2016 after a design change and could potentially stir up further privacy issues, which have plagued the social media site.

Speaking to Reuters, a spokesperson for Facebook said that the contacts were “not shared with anyone” outside of Facebook and that they were “deleting them,” adding that any users affected by this would be notified. The issue has been defined as an “underlying glitch,” which the company says it has now fixed.

The company has also said it did not realize what was happening until recently.

“When we looked into the steps people were going through to verify their accounts, we found that in some cases people’s email contacts were also unintentionally uploaded to Facebook when they created their account.”

Business Insider reported on the “glitch” earlier, saying that contacts were being “harvested” without users knowing about it and that a message would appear on the screen which would indicate that the site was “importing” contacts before people had given their consent.

CNN says that Facebook made changes to its verification process when a user signs up for an account. Before the change, users were able to upload their email contacts so they could find their friends on the site quickly. Facebook then changed the language which explained that their contacts would be uploaded. As a result, it was unclear to many that contact lists would be uploaded, which meant the site was doing so without users’ consent.

Former chief technology officer for the Federal Trade Commission, Ashkan Soltani, tweeted on Wednesday evening that this could be one of the most “legally actionable behaviors” by the site, adding that he was confident that “regulators will be taking a look.”

This is not the first time Facebook has come under scrutiny for privacy issues. In 2018, the U.K. political consulting firm Cambridge Analytica had obtained millions of people’s personal information without their knowledge.

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The site was also criticized recently when the New Zealand shooter live streamed to Facebook the March 15 attack on two mosques in Christchurch.

The site currently hosts around 2 billion users across the globe and is considered the biggest social networking site online. CEO of Facebook Mark Zuckerberg has made promises to focus more on privacy concerns by encrypting messages and implementing better security systems on the platform.