Marc Rotenberg, a legal professor at Georgetown law school and director of the Electronic Privacy Information Center, told Reuters the new feature was "troubling."
"There is a strong echo of the Google Buzz snafu," he said, referring to the social networking service that Google launched in 2010. It was discontinued in 2011 following privacy concerns regarding the use of Gmail users' contact details to create social networks that were viewable by all.
It comes amid pre-existing concerns about the ability of Google Plus users to add somebody else as a contact without the consent of that person. By contrast, users of social network Facebook, for instance, must approve all "friend" requests.
The new feature will be rolled out over the next few days. Google said users would get an email with information and a link to the setting when the update was ready.
(Read more: U.K. users sue Google for alleged breach of privacy)
In the U.S. however, Google is under pressure to monitor its social network more closely following allegations of inappropriate behavior by users. Lobbying group Consumer Watchdog has described Google Plus as a "virtual playground for online predators and explicit sexual content" and called on Google to ban offending users.
—By CNBC's Katy Barnato. Follow her on Twitter @KatyBarnato