Several big companies are posting recruitment ads on Facebook which are only visible to a certain age group and selectively exclude older workers from seeing those job postings, an investigation has revealed.

The joint investigation by US-based non-profit organisation ProPublica and The New York Times found companies like Verizon, Amazon, Goldman Sachs, Target and Facebook place recruitment ads limited to particular age groups.

“The ability of advertisers to deliver their message to the precise audience most likely to respond is the cornerstone of Facebook’s business model. But using the system to expose job opportunities only to certain age groups has raised concerns about fairness to older workers,” the report said on Wednesday.

“It’s blatantly unlawful,” Debra Katz, a Washington-based employment lawyer said.

The US Federal Age Discrimination in Employment Act prohibits bias against people 40 or older in hiring or employment.

“We completely reject the allegation that these advertisements are discriminatory,” Rob Goldman, a Facebook Vice President, told ProPublica.

Some companies defended their targeting as a part of a broader recruitment strategy that reached candidates of all ages.

“We recently audited our recruiting ads on Facebook and discovered some had targeting that was inconsistent with our approach of searching for any candidate over the age of 18. We have corrected those ads,” said Nina Lindsey, a spokeswoman for Amazon.

Facebook this year launched a section of its platform devoted to job ads.

“Facebook allows advertisers to select their audience, and then Facebook finds the chosen users with the extensive data it collects about its members,” the report added.

After courting controversy for enabling Russia-controlled accounts to buy ads before the 2016 US presidential election, it also came to light that the social network also enabled advertisers to reach “Jew haters”.

Facebook enabled advertisers to direct their pitches to the news feeds of almost 2,300 people who expressed interest in the topics of “Jew hater”, “How to burn jews”, or “History of why jews ruin the world”, an earlier ProPublica investigation had revealed.

After ProPublica, a recipient of the 2017 Pulitzer Prize for public service, contacted the social media giant, it removed the anti-Semitic categories.

Facebook COO Sheryl Sandberg — also of Jewish origin – later apologised, saying the company is now strengthening its ad policies.

“The fact that hateful terms were even offered as options was totally inappropriate and a fail on our part. We removed them and when that was not totally effective, we disabled that targeting section in our ad systems,” Sandberg wrote in a blog post.

“If someone self-identified as a ‘Jew-hater’ or said they studied how to burn Jews in their profile, those terms showed up as potential targeting options for advertisers.

“Seeing those words made me disgusted and disappointed – disgusted by these sentiments and disappointed that our systems allowed this. Hate has no place on Facebook and as a Jew, as a mother and as a human being, I know the damage that can come from hate,” she added.

Facebook recently acknowledged that Russian-controlled pages and accounts spent $100,000 on ads meant to “amplify divisive social and political messages” before the US presidential election.

Another recent ProPublica probe found that Facebook allowed housing advertisers to target audiences by race and exclude minorities, raising questions about whether the company is in compliance with federal fair housing rules that prohibit such discrimination.