Google is to take on the US government in court today as the Internet search engine fights demands to hand over records and lists of data.
The Justice Department wants Google to provide a week's worth of search records, saying it needs the data to help it better police cyberspace.
But Google complains that complying with the request would compromise its business and the privacy of its users.
Similar requests were made of other net firms such as Microsoft, Yahoo and AOL.
Head to head
The case has focused attention on the issue of personal information held by Internet companies.
The US government is seeking to defend the 1998 Child Online Protection Act, which has been blocked by the Supreme Court because of legal challenges over how it is enforced.
It wants the data from the search engines to prove how easy it is to stumble over porn on the net. If it can prove this, the result might be onerous regulation for many websites.
Officials said it had tried to generate the same information using the Internet Archive website but did not get the results it wanted.
The BBC's North America business correspondent Guto Harri said that Google's refusal was based on three main arguments.
Firstly, Google says it does not want to do the government's work for it, and secondly it says that it wants to protect its product. Thirdly, Google wants to show users that the company is serious about protecting their privacy.
Google also argued that the government's position is flawed and that the search data would not help them in dealing with problems such as child pornography.
Co-operating with the government "is a slippery slope and it's a path we shouldn't go down," the Google co-founder Sergey Brin told industry analysts earlier this month.
The company's stance has been supported by the American Civil Liberties Union.
Lawyers for the Department of Justice and Google are scheduled to present their arguments in San Jose later today.