Details of user e-mails, website visits and net phone calls will be stored by internet service providers (ISPs) from Monday under an EU directive.
The plans were drawn up in the wake of the London bombings in 2005.
ISPs and telecoms firms have resisted the proposals while some countries in the EU are contesting the directive.
Jim Killock, executive director of the Open Rights Group, said it was a "crazy directive" with potentially dangerous repercussions for citizens.
All ISPs in the European Union will have to store the records for a year. An EU directive which requires telecoms firms to hold on to telephone records for 12 months is already in force.
The data stored does not include the content of e-mails and websites, nor a recording of a net phone call, but is used to determine connections between individuals.
Authorities can get access to the stored records with a warrant.
Governments across the EU have now started to implement the directive into their own national legislation.