Apple and Google are temporarily stopping workers listening to voice recordings captured by smart speakers and virtual assistants.
It follows a Guardian report that third-party contractors used by Apple had heard people having sex and discussing private medical information.
Siri and other services can activate in error after wrongly picking up sounds they mishear as their “wake” words.
Apple said the move would affect users worldwide.
Google suspended the practice across the EU on 10 July but has only just confirmed the fact in public.
Amazon – which also uses staff to transcribe some recordings – has not commented.
Technology companies use staff to “grade” voice recordings to improve their virtual assistants’ accuracy rates in handling requests – and take steps to anonymise the source.
Google, for example, distorts the recording before it is listened to in order to disguise the user’s voice.
However, many members of the public were unaware of the practice until theBloomberg news agency reported the fact earlier this year.
“We are committed to delivering a great Siri experience while protecting user privacy,” Apple said in a statement.
“While we conduct a thorough review, we are suspending Siri grading globally.”
The company added in the future users’ voice recordings would not be included in the grading process unless they had chosen to opt in.
Germany’s data protection commissioner in Hamburg has also launched an investigation into Google over the practice, with which the search company is cooperating.