Facebook should stop unsolicited advertising to users in Nordic countries or face legal action, the Norwegian consumer agency said on Thursday.
The agency, like its counterparts in the Nordic region, wants to put an end to the unsolicited advertisements that appear on users' news feeds.
It has sent a letter to the European Commission to determine whether Facebook is in line with the EU's directive on privacy and electronic communication -- and possibly to make amendments to rules drawn up before Facebook was founded.
"It is prohibited to send electronic advertisements to consumers who haven't given their consent, either by email or SMS," consumer mediator Gry Nergaard told AFP.
"We think that some of the advertising that Facebook calls 'sponsored stories' is beginning to look like unsolicited electronic messages," she said.
Depending on the response from European authorities and Facebook, Norwegian officials may undertake legal action to put an end to the practice.
"Sponsored stories" are advertisements that show up on a Facebook user's page informing him or her that one of his contacts, or "friends", whose name and or photo may also appear, "likes" a product, giving the false impression that the product or company is being endorsed by the friend.
"It has evolved even further," Nergaard said. "Now you can receive an advertisement without the mention that your friend 'liked' it," she said.
Facebook, which is hugely popular worldwide but is struggling to generate advertising revenue, claims it is abiding by European and Norwegian laws.
Its spokesman in northern Europe, Jan Fredriksson, said users could choose to block this type of advertising in their settings.
But Nergaard said it was not enough to provide an "opt out" option, the key issue was that Facebook did not have users' prior consent.
The European Commission was to examine the issue in the near future, she said.
Facebook in June settled a $10 million lawsuit from users in the US who claimed their names, images and other information were improperly used in "sponsored stories".