Maricopa County Sheriff Joe Arpaio is now the target of a federal grand jury probe, according to the Maricopa county manager.

Manager David Smith tells 12 News he has been called as a witness in the investigation, as well as Deputy County Manager Sandi Wilson.

Sources say the investigation is tied to allegations of abuse of power relating to targeting political opponents and enemies for harassment and investigation. Smith says that includes threatening investigations against opponents when there is no probable cause and intimidating county employees at their homes.

Sources told 12 News late Thursday that the U.S. Department of Justice in Washington has been conducting and managing the investigation, which started more than a year ago. It started late in George W. Bush's Administration, stopped during the transition, and started again after President Obama took office.

Sources say local FBI agents have been gathering the evidence and, the FBI has informed potential witnesses that they should not speak to the media about this issue.

Sheriff Arpaio's spokeswoman Lisa Allen told 12 News that the sheriff has not been notified by federal officials whether or not he is the subject of a federal grand jury investigation. Allen said as far as the sheriff is concerned, it will be business as usual.

Maricopa County Attorney Andrew Thomas' office told 12 News that it is unaware of any investigation of Sheriff Arpaio.