A case debating the legality of India's unique Aadhaar biometric ID began this week in the Supreme Court.
Privacy activists have said the rights of citizens would be compromised once Aadhaar was made compulsory and that it could be a tool to keep citizens under surveillance through their life.
The Aadhaar system uses fingerprints and iris scans to provide users a 12-digit unique identity number they can use to access government and other services.
Appearing for former Karnataka HC judge KS Puttaswamy and other social activists, senior advocate Shyam Divan contended that no democratic country had adopted such scheme as it is the antithesis to the very principle of people's rights and liberty.
He said Aadhaar could become an instrument of oppression and exclusion at the hands of the government, which must not be allowed.
"The petitioners are certain that if the Aadhaar Act and programme is allowed to operate unimpeded, it will hollow out the Constitution, particularly the great rights and liberties it assures to citizens," Divan said.