HARRISBURG - Fresh off his victory in Tuesday's Republican gubernatorial primary, Attorney General Tom Corbett has stepped into a political minefield by using grand-jury subpoenas to try to unmask two of his harshest critics on the Internet.

Earlier this month, Corbett's office subpoenaed the online social networking site Twitter Inc., seeking identifying data on "CasablancaPA" and "bfbarbie." Both daily excoriate Corbett and his office's long-running political-corruption investigation known as Bonusgate.

The subpoena was apparently part of prosecutors' efforts to show one Bonusgate defendant's lack of remorse as he awaits sentencing.

But news of the subpoena unleashed a cascade of criticism from First Amendment and electronic-privacy advocates, who contend that Corbett is engaging in a Big Brotherlike attempt to silence and intimidate people who don't agree with him.

Twitter, based in San Francisco, has declined to turn over the information. The ACLU of Pennsylvania says it will seek to quash the subpoena on behalf of the two anonymous tweeters.

The issue promptly entered the governor's race, with Corbett's Democratic opponent, Dan Onorato - fresh from his own primary victory - saying in Philadelphia that he found it "outrageous" and "unbelievable" that the attorney general would use the powers of his office to subpoena critics.

Corbett, in Hilton Head Island, S.C., for his daughter's wedding Friday, could not be reached for comment.

Kevin Harley, spokesman for the Attorney General's Office, said the subpoena had "nothing to do with limiting critics." He said the office's intent would become clear Friday morning, when Bonusgate defendant Brett Cott has been scheduled for sentencing.

Harley declined to elaborate, citing the secrecy of grand-jury proceedings. But a sentencing memorandum in Cott's case, filed in Dauphin County Court, contained clues: Prosecutors from Corbett's office argued that Cott, who was convicted in March on three of 42 corruption charges, is CasablancaPA.

The prosecutors contended that Cott has shown little remorse for his crimes, as evidenced (among other things) by his alleged postings as CasablancaPA. In addition to being a Twitter account, CasablancaPA is also a blog dedicated to, as it puts it, "exposing the hypocrisy of Tom Corbett."

The prosecutors contended that Cott had used the blog to "deflect blame and deny responsibility for his criminal conduct, and to attack and malign the investigative and prosecutorial process which resulted in his conviction."

They also cited what Cott told reporters after his March 22 conviction on three counts and acquittal on 39 others: "That's it? That's the best he [Corbett] can do? I hope this helps him get elected governor."

Cott's lawyer, Bryan Walk, called the argument about blog postings "ridiculous."

Even if Cott did write the blog, Walk said Thursday, "who cares? It's not criminal, it's not illegal, and it's not improper."

He added: "For them to say, 'Judge, you should whack him for not being contrite,' is crazy. And it's them trying to save face because they got their a- handed them at trial."

Cott was one of 12 Bonusgate defendants, all connected to Democrats in the state House, accused of conspiring to use state money for political campaign work. Seven of the 12 pleaded guilty; Cott and two others - including onetime House Democratic Whip Mike Veon - were convicted; and two were acquitted.

Prosecutors are seeking a sentence for Cott of 18 to 24 months in prison. His lawyer is pushing for probation.

Contacted via e-mail, both CasablancaPA and bfbarbie declined Thursday to reveal their identities.

A writer on CasablancaPA who goes by "Signor Ferrari" - the unctuous fictional character portrayed by Sydney Greenstreet in the 1942 film Casablanca - e-mailed that he wished to stay anonymous because "we have a constitutionally protected right to criticize public officials anonymously, as do all Americans."

In a lengthy e-mail, bfbarbie said: "I am scared. Scared that a BIG, POWERFUL politician could do such [a thing] to a little person like myself just for talking/twittering."

The ACLU of Pennsylvania is representing the two anonymous tweeters and will try to get the subpoena quashed if an agreement cannot be reached with Corbett's office to withdraw them, said attorney Witold Walczak.

"Anytime you've got the government officer using a subpoena to unmask a political critic, it raises serious First Amendment concerns," Walczak said. "It is a prized American possession to criticize the government and to do so anonymously in the tradition of the Federalist Papers and Mark Twain."

Told that Corbett was using the subpoena to gather information for sentencing purposes, Walczak said: "Using the grand-jury process to get evidence in the aid of sentencing is an abuse of the system. Grand juries are to investigate potential crimes, not aid in prosecution."

John Morris, general counsel for the nonprofit Center for Democracy and Technology, based in Washington, said most previous attempts to pierce the anonymity of Internet posters have emanated from businesses that want to fight anonymous critics.

"It's an outrageous and astounding abuse of power and one that plainly violates the First Amendment and will not be upheld in court," Morris said Thursday. "There's a clear constitutional right to anonymous speech."

More than a decade ago, a Pennsylvania court ruled in one of the earliest cases involving anonymous online criticism of public officials. In that 1999 case, a state Superior Court judge sued to learn the identity of an anonymous online critic who accused the judge of improper conduct.

The Pennsylvania Supreme Court found that anonymous political speech was protected by the First Amendment.

Contact staff writer Angela Couloumbis at 717-787-5934 or acouloumbis@phillynews.com.

Inquirer staff writers Jeff Gelles and Tom Infield contributed to this article.