HARRISBURG - Gov. Rendell was among at least 30 governors to receive a letter this week from an extremist antigovernment group demanding that he resign or face being "removed from office," according to officials in the Philadelphia office of the FBI.

Rendell received the letter within the last 48 hours and immediately turned it over to federal authorities, FBI Special Agent J.J. Klaver said.

Klaver said the letter was from a so-called sovereign citizens group that is "advocating a plan to remove all state governors from office."

"These are individuals who reject all forms of government authority, and they believe they are emancipated from all the responsibilities associated with being U.S. citizens, such as paying taxes and obeying laws," Klaver said.

Klaver stressed that although such groups have advocated violence or other illegal acts, the letter sent to Rendell did not.

"It did not say, 'We are going to kill you,' " Klaver said. "It said, 'You have to vacate your office or you will be removed from office.' "

He said the letter was lengthy and contained petitions with signatures from people who presumably support the call for governors to resign. He would not elaborate on the name of the group, how large it was, or details in the letter.

Rendell's office declined to comment.

Mike Drewniak, spokesman for New Jersey Gov. Christie, said, "It does not appear that we've received such a letter, but we are aware of the matter, as is the wider state and federal law enforcement community."

Ed Myslewicz, spokesman for the Pennsylvania Department of General Services, which oversees the Capitol Police, said, "We have increased our vigilance within the Capitol complex. We continue to watch, to monitor, to screen visitors entering the building, and we continue our use of bomb dogs as well as our use of bicycle patrols."

In Nevada, the capitol in Carson City was locked down late Tuesday as a precaution after its capitol police received a similar letter, according to a news report in the Nevada Appeal.

The newspaper reported that all but the main entrance to the capitol were locked and that metal detectors were set up to screen visitors and packages. Large boulders were placed at ungated entrances to the capitol grounds.

The Nevada Governor's Office could not be reached for comment Thursday.

The threat was not the first for Rendell. In December 2008, the governor's mail room was evacuated for almost an hour as FBI agents investigated an envelope addressed to the governor that was leaking a white powder.

The substance, it turned out, was infant cereal, part of a larger hoax in which similar envelopes were sent to governors in 45 other states, as well as 15 U.S. embassies.

That same year, Rendell received a threatening e-mail from a Blair County man who was later arrested.