Google — which a year ago vowed to clamp down on Gmail users' privacy — has reportedly been letting outside app developers scan millions of inboxes, according to a Wall Street Journal examination.

Despite the promise from Google last June to stop scanning Gmail messages for the purpose of selling targeted ads, the tech giant has been allowing hundreds of outside software developers to access inboxes, the Wall Street Journal reported on Monday.

The app developers were reportedly granted access to the inboxes of users who signed up for email-based tools, such as price comparisons or travel-itinerary planners, the Journal said. By opting in to those tools, users were potentially exposing entire Gmail messages, email addresses, and other pieces of information to third parties, it added.

Allowing artificial intelligence to scan inboxes is fairly common. But the Journal claimed that it's not just computers looking through emails: in some cases, human employees at the third parties have also been scanning users' Gmails, the paper said.

And the consent form that Gmail users must sign to allow outside apps to connect to their inboxes does not explicitly spell out that actual people might be peeking at their private messages, it said.

NBC News could not independently verify the Wall Street Journal's report, and Google did not immediately respond to an inquiry for comment.

But Google told the Journal that it only provides data to outside developers who have been vetted. And data is only from users who have explicitly granted permission to access their email.

In a statement, it also said Google's own employees read emails only "in very specific cases where you ask us to and give consent, or where we need to for security purposes, such as investigating a bug or abuse."

The allegations come amid loud calls for data privacy following revelations of improper sharing of user data by Facebook during the 2016 election, as well as the social network's handling of the scandal.

Last week, Facebook and Twitter launched new transparency tools ahead of the midterm elections, giving the public an unprecedented, behind-the-scenes look at what ads are being run on their services.

Also last week, California passed the country's strongest data privacy law yet, requiring big tech companies including Facebook, Google and Amazon to disclose what data they are collecting about consumers and with whom they are sharing the information.

With 1.4 billion users, Gmail is the most popular email service in the world. This is hardly the first privacy violation it has been accused of: When Gmail launched in 2004, it caused an uproar by displaying ads at the top of users' inboxes that used keywords from their emails to advertise related products.

The service has also been subject to several lawsuits in regards to its privacy policy throughout the years.