Common Pleas Court Judge John M. Cleland is hearing the case because of McCaffery's close ties to the court system in Philadelphia, where he began his judicial career. Cleland did not rule on The Inquirer's preliminary objections.
Neither Carrie Adamowski, an FBI spokeswoman, nor Patricia Hartman, spokeswoman for the U.S. Attorney's Office in Philadelphia, would confirm or deny any investigation.
McCaffery could not be reached for comment.
McCaffery and Rapaport filed suit in March in Philadelphia Common Pleas Court, contending they were defamed by a series of stories in The Inquirer between March and August 2013.
The series, by reporter Craig R. McCoy, concerned fees Rapaport received for referring clients to personal-injury law firms. In addition to being a lawyer, Rapaport has served as her husband's chief legal aide for much of the last 16 years.
The Inquirer reported that firms with which Rapaport had a financial relationship appeared before the Supreme Court 11 times on unrelated cases. McCaffery, the paper reported, did not disclose those ties in court.
The newspaper then reported that the FBI had begun an investigation into the matter.
The defamation lawsuit maintained that McCaffery and Rapaport did nothing illegal nor unethical and that the series tarnished their reputations.
Inquirer editor William K. Marimow, a defendant in the lawsuit with McCoy, has called the series "accurate, thorough, and fair," and one that examined an "issue of public importance in the administration of justice in the state of Pennsylvania."
The high court's chief justice, Ronald D. Castille, quoted in the series with other legal experts, said he considered the financial relationships a potential conflict of interest.
After the articles' publication, the Supreme Court adopted rules prohibiting judges from hiring relatives or sitting on corporate boards.