Google and Facebook on Monday fought in the Delhi High Court to quash criminal charges that they are responsible for obscene online content.
The companies, which are set to be joined in their action by Microsoft and Yahoo!, have filed petitions asking for a lower court case brought by a local journalist against 21 Internet firms to be stayed.
On Friday, the Indian government gave its sanction for the firms to be tried for serious crimes such as fomenting religious hatred and spreading social discord, offences that could land company directors in prison.
Lawyers acting for the search engine and social networking site told Delhi High Court Justice Suresh Kait that they were not responsible for material posted by users on their platforms.
"Search engines such as Google cannot control websites being searched by users," Google-India's lawyer Neraj Kishan Kaul told the packed court.
"(The) summons reflects a complete lack of understanding in how it works," Kaul told the judge, referring to a summons issued to the Internet companies by a lower criminal court on December 23.
Kaul also insisted that Internet companies could not be held responsible for filtering content.
"There are serious constitutional issues of freedom of speech," the lawyer said.
Facebook India's lawyer Sidharth Luthra said evidence presented against the defendants by the complainant, 39-year-old journalist Vijay Rai, needed to be "tested" before it could be admitted at trial.
Rai has submitted a compact disc of evidence he says was taken from the Internet that risks causing religious strife."Unlike search engines, Facebook is a closed group and even as we trying to create a global community we try and respect local laws," Luthra told the judge, adding that Facebook has safeguards against abuse and obscenity.
Google and Facebook's lawyers told the court that they act to remove content deemed to contravene laws in the countries in which they operate.
The government's sanction to prosecute at the weekend represents an escalation of a recent tussle between social networks and government officials, in particular Communications Minister Kapil Sibal.
Sibal last month pledged a crackdown on "unacceptable" online content and urged the social networks to exert more control over the photos, videos and users' comments uploaded on their platforms.
The trial will resume on Thursday.