Spanish officials have taken Google to the European Court of Justice in a bid to force the search giant to delete information that breaches a person's privacy.
U judges will begin hearing arguments today in a case brought by Spain's data protection authority that could have serious consequences for online freedom of information laws and the protection of individual privacy.
It is based on a complaint from a Spanish man who searched for himself on Google and found a years-old newspaper report that said his house was being auctioned because he had not paid his taxes.
Google argues that it should not be required to erase lawful content from its search index. However, the Audiencia Nacional, one of Spain's top courts, upheld the man's complaint and ordered Google to delete the information.
The case was referred to the Court of Justice in March last year after Google challenged the decision.
Supporters say that if Google is asked to delete such information it will create a slippery slope leading to all sorts of data being deleted for spurious reasons, and would essentially make Google responsible for the content it indexes.
The European Court will try to determine if Google can be considered the "controller" or just a host of information. It will also assess whether a search engine run by a company based in California such as Google can be subject to EU privacy law.
Spain's data regulator has said EU judges must consider if EU citizens have to go to US courts to exercise their privacy rights and whether Google "is responsible for the damage the diffusion of personal information can cause for citizens".
The hearing will also test a draft European law that aims to strengthen citizens' privacy. The rules proposed by the European Commission in 2012 and being debated by the European Parliament would give people "the right to be forgotten" - that is, the right to have personal data deleted, in particular from the web.
The proposal has sparked sharp criticism from industry experts who say Internet content could be manipulated at the expense of freedom of speech if such a principle were to be enshrined in European law.
The case is expected to last for up to a year.