Google is vowing to "vigorously" fight a legal challenge from the US Justice Department seeking to force the company to reveal details about what users are searching for.
The Internet search engine company has refused to comply with a White House subpoena first issued last summer, where Google was asked for a list of all requests entered into it's search engine over a week and information on the websites included in its index.
US Attorney General Alberto Gonzales this week asked a federal judge in San Jose for an order to hand over the requested records.
The Bush administration claims the information is vital in its effort to restore online child protection laws that have been struck down by the US Supreme Court.
Although the government says it isn't seeking any data that ties personal information to search requests, the subpoena still raises serious privacy concerns, experts have warned.
Those worries have been magnified by recent revelations that the White House authorised eavesdropping on civilian communications after the September 11 attacks without obtaining court approval.
"Search engines now play such an important part in our daily lives that many people probably contact Google more often than they do their own mother," said Thomas Burke, a San Francisco attorney who has handled several prominent cases involving privacy issues.
The content of search request sometimes contain information about the person making the query.
Every other search engine served similar subpoenas by the Bush administration has complied so far, according to court documents. The cooperating search engines weren't identified.