Voice-driven digital assistants Alexa, Siri, and Google Assistant have served as a massive convenience in millions of homes worldwide.

But reports of humans listening in on user interaction with digital assistants have raised fears over violations of data privacy. At least one German institution is already probing the issue, with regulators from other countries in tow.

Here is an excerpt from a story published in Health Data Management:

Apple and Google, which is currently being investigated by Hamburg’s data protection authority, have both suspended their programs; Amazon has announced changes to its terms that let users opt out of human review of their recordings. Regulators from Ireland and the United Kingdom are now also looking into whether the tech giants have infringed European privacy regulations.

“We are aware of privacy concerns relating to voice assistant programs and will be assessing the available information,” said a spokeswoman for the Information Commissioner’s Office, the U.K.’s data protection regulator. She added the ICO would discuss the matter with the board of European data protection authorities “in order to ascertain the full facts and any possible risks to the rights of U.K. residents.”

Bloomberg first reported in April that Amazon had a team of thousands of workers around the world listening to Alexa audio requests with the goal of improving the software. Their tasks include listening to and transcribing voice recordings. Some of the workers reviewing customer recordings had access to certain personal data, including users’ first names and their location.

At the time, Amazon and people familiar with the program said only a small sample of recordings were manually reviewed. Bloomberg reported that similar human review is used for Alphabet’s Google Assistant and Apple’s Siri. Recent news reports elaborated on the extent of those companies’ review program.

The reports sparked concern among privacy advocates that the practice could violate users’ rights, particularly in cases where devices begin recording unintentionally or without the user’s knowledge.