The social media giant came under fire earlier this month after it emerged that it had hired hundreds of third-party contractors to transcribe clips of audio sent via its Messenger app. - AFP or licensors

Facebook could come under fresh scrutiny over privacy concerns after the company admitted that audio clips sent by some users in Europe had been collected and transcribed without their consent.

The social media giant came under fire earlier this month after it emerged that it had hired hundreds of third-party contractors to transcribe clips of audio sent via its Messenger app.

Audio can be generated by the app’s voice chat function, which allows users to send voice notes to each other. These messages are then transcribed by artificial intelligence in a written form for the recipient.

Facebook claimed the work had been stopped “more than a week” before the reports, and that the people paid to listen to audio clips were only checking anonymised files to ensure transcription was taking place correctly on its Messenger app.

The company originally stated that users in the European Union were unaffected, as their voice notes had not been listened to.

But following a review of the programme, Facebook has been forced to inform EU regulators that up to 50 citizens across 14 countries in the 28-member state bloc were involved.

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Facebook initially claimed that only US users were affected, but audio messages sent to US users meant some EU citizens were pulled into the trial.

The EU has taken a tough stance on the handling of data privacy by tech firms in recent months. Facebook’s admission makes it the latest Silicon Valley firm caught listening to user messages without explicit consent after similar activities were found at the likes of Apple, Google and Amazon.

On Monday, it emerged that Facebook was being investigated by the data protection authority in Hamburg, Germany, over the transcription of audio. The authority is already looking into Google’s automatic speech assistant that converts audio into text.

Facebook did not respond immediately to a request for comment.