The American Civil Liberties Union is to help two Twitter users fight to keep their identities secret after they tweeted criticism of Pennsylvania attorney general Tom Corbett.
The two are the subject of subpoenas from a state-wide investigative grand jury in relation to an investigation into former Democratic legislative aide Brett Cott, recently convicted of public corruption charges.
He's alleged to have taken advantage of legislative employees and government resources to run his political campaigns.
The two Twitter users, CasablancaPA and bfbarbie, have been highly critical of Corbett, and there have been suggestions that the posts actually originated from Cott, leading to the subpoenas.
A sentencing memorandum accused him of having "extensively and anonymously utilized" the CasablancaPA blog "to deflect blame and deny responsibility for his criminal conduct".
So far, Twitter has refused to reveal the identities of the two.
But the ACLU says the subpoenas violate First Amendment rights. It's asked Corbett's office to withdraw them, and says it plans to file a motion to quash them if Corbett refuses.
Using a grand jury to reveal the identities of political critics is "unconstitutional retaliation that violates the First Amendment", said Vic Walczak, legal director for the ACLU of Pennsylvania.
CasablancaPA says the daily traffic on http://casablancapa.blogspot.com/ has risen ten-fold since the subpoenas were issued.