Harvard law professor Alan M. Dershowitz is to advise the Wikileaks team over US government action involving the whistleblower site.
Dershowitz was appointed by the head of Julian Assange's UK legal team, Geoffrey Robertson QC, to advise on a case involving the US government and Twitter.
US prosecutors are seeking to obtain details about Wikileaks and its Twitter followers from the micro-blogging site.
"I will be focusing on the First and Fourth Amendment issues and will follow Robertson's lead," Dershowitz told ZDNet UK on Tuesday.
The US first amendment deals with freedom of speech, while the fourth amendment deals with freedom from unreasonable searches.
Wikileaks editor Assange said that the request for information, which began to be heard before a Virginia magistrate's court on Tuesday, infringed Twitter customers' privacy rights.
"This is an outrageous attack by the Obama administration on the privacy and free speech rights of Twitter's customers — many of them American citizens," said Assange in a Wikileaks statement posted to TwitLonger on Monday.
The US Department of Justice obtained a court order on 14 December, 2010, that required Twitter to hand over details of communications between Wikileaks and its followers, said the statement. The order was granted under provisions of the US Patriot Act, which was designed as anti-terrorist legislation.
Wikileaks said that other organisations, including Google, Facebook, and Yahoo, may have been approached to hand over information to the US government.
On Tuesday, Google declined to say whether it had given the US government any information pertaining to Wikileaks. Facebook and Yahoo had not responded to a request for comment at the time of writing.
Assange is currently fighting extradition from the UK to Sweden for questioning about sex-crimes allegations.