Google will this week challenge a Spanish demand to remove links to articles in newspapers, including El País, and official gazettes, that the subjects have complained breach their privacy.
The technology giant has been ordered to remove almost 100 online articles from its search listings by Spain's data protection authority, which Google warns would have a "profound, chilling effect" on freedom of expression.
Google will challenge the orders in a Madrid court on Wednesday, the outcome of which could set a controversial new precedent for internet publishing in Spain.
An injunction against search engines is the only way to block access to sensitive material published by these sites, the Spanish authority argues, as newspapers in the country can legally refuse to comply with more informal requests.
However, Google says it acts only as an intermediary, and therefore it cannot be held responsible for all content on the internet.
Peter Barron, Google's director of external relations for Europe, told the Guardian: "We are disappointed by the actions of the Spanish privacy regulator. Spanish and European law rightly hold the publisher of the material responsible for its content.
"Requiring intermediaries like search engines to censor material published by others would have a profound, chilling effect on free expression without protecting people's privacy."
Cases covering five disputed articles will reach the Madrid magistrates' court this week. Google will be ordered to remove the articles from its search results if its court challenge is unsuccessful. However, the articles would still be available on the newspaper websites should Google lose.
The demands follow a burgeoning public debate in Spain about "the right to be forgotten" – or the right for people to delete their internet "data trails". Complaints from the public about their representation online have jumped 75% year on year, the country's privacy regulator said in June last year.
Padraig Reidy, news editor at Index on Censorship, said the ruling would have "massive ramifications" for freedom of expression. "What's worrying is why they should go to Google, rather than the people who are putting up this content – some of which is legally bound.
"It encroaches on privacy law, and has massive ramifications on freedom of expression and how the internet works. If Spain is punishing search engines for indexing content how can there be freedom of expression? It looks like a plan by people who don't know how the internet works."
Spain's Agencia Española de Protección de Datos – the national data protection agency – declined to comment.