Prosecutors investigating U.S. Rep. Chaka Fattah asked a three-judge federal appeals panel Monday to give them access to seven years of his private e-mails, a position Fattah's lawyer argued violates the protection the Constitution provides Congress.

Fattah's attorney, Luther E. Weaver III, backed by House general counsel Kerry W. Kircher, argued that the U.S. Court of Appeals for the Third Circuit panel should block Google Inc. from immediately releasing e-mails that prosecutors have subpoenaed.

All references about the holder of the e-mail account were cloaked in the pseudonym of "Congressman Smith" because most records in the case are sealed under a federal court order. The appeal was labeled as "the search of electronic communications (both sent and received) in the account John at Internet service provider Google Inc."

But it was clear from the statement in the hearing that Fattah's e-mail account was at issue.

In March, Fattah, a Democrat, just starting his 11th term in Congress, notified House Speaker John Boehner that prosecutors in Philadelphia were seeking documents from his congressional offices.

Two former Fattah confidants pleaded guilty last year to federal charges in what has been described as an ongoing federal investigation. Sources familiar with the investigation say Fattah is the focus of the probe.

The same prosecutors who have been identified as overseeing the Fattah investigation were listed in the appeals court docket.

At Monday's hearing, Circuit Court Judges Thomas L. Ambro, Julio M. Fuentes, and Jane Richards Roth intensely questioned Weaver, Kircher, and Assistant U.S. Attorney Robert A. Zauzmer about the protection that members of Congress have under the Constitution's "speech or debate clause."

When one judge asked about the congressman's being a "target" of the federal investigation, Weaver corrected the judge to say that his client was only the "subject" of the ongoing criminal investigation.

The term target is used for a person who has received a "target letter," which prosecutors typically send shortly before a person is indicted.

Weaver said he learned of the prosecutors' subpoena for the e-mails dating back to 2008 after Google told his client that federal investigators had asked for them.

He told the judges that his client should be allowed to review the e-mails, rather than letting investigators immediately have them. He said the e-mails also should be reviewed by a lawyer to prevent the release of information involving attorney-client privilege.

Zauzmer argued that delays could damage the federal investigation because of problems with the statute of limitations.

The docket shows the appeal has been underway since August. It stems from an appeal that was filed from a U.S. District Court case in Philadelphia that is also under seal.

Stanley Brand, a former House counsel and prominent Washington defense lawyer, said fights over lawmakers' e-mails are often litigated.

Legislative activity - and documents related to that activity - are protected by the speech or debate clause, which is meant to prevent the executive branch from intimidating lawmakers.

"Legislative activity isn't all-encompassing," Brand said, but "it reflects a significant portion of what Congress does."

"If these e-mails relate to legislating, debating, committee reports, or things that members generally do in connection with the legislative process, then they are protected. Their release can't be compelled," Brand said.

When House lawmakers are subpoenaed, they present the demands to the House's general counsel, who reviews the subpoenas and decides whether the requested information is privileged. A panel made up of leaders from each party can authorize the House counsel to fight a subpoena, or part of one, in court. The House fiercely protects its rights.

"At some level it's not just his privilege, it's the privilege of the body," Brand said.

Legislative activity, Brand said, is protected regardless of whether Fattah was using his official e-mail account or not. As to why a lawmaker would use a private e-mail account for official work, Brand said, "It's complicated, because these guys have three lives: a political life, an official life, and a personal life. What they're constantly trying to do is divide themselves along those lines. It's not always clear and it's not always easy."

Prosecutors, though, have often chafed at how zealously and, in their view, broadly the House has interpreted the protections of the speech or debate clause, even if acting on principle.

"I always felt that one of their principles ought to be that we don't want people who commit felonies as sitting members of the House," said Andrew Levchuk, a former federal prosecutor who helped convict one-time U.S. Rep. Rick Renzi (R., Ariz.).

Fattah, in a December interview, told The Inquirer that "we're doing everything that lawfully is permitted in terms of our cooperation. We do have some responsibilities as a member of the House that you are well aware are not unique to me."

He added, "This is being handled by lawyers - all of the review of documents is being done outside of my purview. I have no involvement whatsoever."

If Fattah's lawyers and the House assert congressional privilege over certain documents, prosecutors might seek a list of e-mails that are withheld, with dates, the sender and receiver, and topics covered, Levchuk said. Fattah's attorneys and the House counsel will likely seek to review any documents requested before they are turned over, he said.

In a letter to the House speaker published in the Congressional Record on March 11, 2014, Fattah wrote that the subpoena "seeks some information that is not material and relevant, and that is 'not consistent with the privileges and rights of the House.' "

He said in the letter he would move to quash the subpoena "to that extent" but otherwise comply "to the extent that it is material and relevant" and in compliance with the privileges of the House.

Parts of the Fattah investigation have already been disclosed in guilty pleas in U.S. District Court last year of former Fattah campaign aides Gregory Naylor and Thomas Lindenfeld.

In those documents, prosecutors painted Fattah, who sits on the Appropriations Committee, as the orchestrator of a scheme to use federal grant money to pay off a $600,000 debt from his 2007 mayoral run.

The plea documents say Fattah, identified only as "Elected Official A," routed taxpayer money to nonprofits run by former staffers, then used that money to pay his campaign debt.