Internet firms will be required to give intelligence agency GCHQ access to communications on demand, in real time.
The Home Office says the move is key to tackling crime and terrorism, but civil liberties groups have criticised it.
Tory MP David Davis called it "an unnecessary extension of the ability of the state to snoop on ordinary people".
Attempts by the last Labour government to take similar steps failed after huge opposition, including from the Tories.
BBC News - Email and web use 'to be monitored' under new laws (external - login to view)