An English local authority said it had forced Twitter to hand over users' details after it took the US microblogging site to court in California, in what is believed the first case of its kind in Britain.
South Tyneside Council, in northeast England, took the legal action in a bid to discover the identity of a blogger, known as "My Monkey", behind allegedly libellous statements against councillors.
"Twitter have released information to our lawyers and this is currently being analysed by technical experts," council spokesman Paul Robinson told AFP.
Details were handed over after the council took Twitter to court in California, where the site is based.
Commentators said the ruling could have implications for the case of footballer Ryan Giggs, whose lawyers have demanded in the British courts that Twitter reveal which users named him over an alleged affair in defiance of a court order.
Ahmed Khan, a South Tyneside councillor, said Twitter had informed him that it was giving his details to the local authority and blasted the situation as "Orwellian."
The website handed over details he had submitted when he signed up for the service, including IP identities, mobile phone numbers and email addresses, he said.
Khan said he believed the council has been given the details of five Twitter accounts, two of which are his.
He denied he was the blogger behind the "Mr Monkey" site: "I'm the kind of person who will tell you face-to-face what I think. I have no need to use an anonymous blog."
Media lawyer Mark Stephens said he believed the case was the first of its kind.
"I am unaware of any other occasion where somebody from this country has actually gone to America and launched proceedings in a Californian court to force Twitter to release the identities of individuals," he told the BBC.
"The implications are that people who have had their name released can actually now go to California and begin proceedings."
MP John Hemming last week outed Giggs as the sportsman who had won an injunction to stop British media reporting his alleged extramarital affair, publicly naming him using a right to freedom of speech in the House of Commons.
Liberal Democrat Hemming argued that the injunction was no longer practical after tens of thousands of people had named the Manchester United star on Twitter.