Websites will soon be forced to identify people who have posted defamatory messages online.
New government proposals say victims have a right to know who is behind malicious messages without the need for costly legal battles.
The powers will be balanced by measures to prevent false claims in order to get material removed.
But privacy advocates are worried websites might end up divulging user details in a wider range of cases.
Last week, a British woman won a court order forcing Facebook to identify users who had harassed her.
Nicola Brookes had been falsely branded a paedophile and drug dealer by users - known as trolls - on Facebook.
Facebook, which did not contest the order, will now reveal the IP addresses of people who had abused her so she can prosecute them.
The new powers, to be added to the Defamation Bill, will make this process far less time-consuming and costly, the government said.
Complying with requests would afford the website greater protection from being sued in the event of a defamation claim.