The Justice Department is seeking to overturn a D.C. Circuit appeals court ruling that the FBI raid on Rep. William Jefferson’s (D-La.) office last year violated the Constitution.

The decision is reopening a separation-of-powers battle over how much protection federal lawmakers should have from government prosecutors’ investigations.

The FBI had obtained a search warrant before the office raid after Jefferson repeatedly rejected subpoenas for materials from his Capitol Hill office. The raid provoked outrage among lawmakers on Capitol Hill and a rare moment of bipartisan comity between GOP and Democratic leaders, who joined forces to fight the raid, during a fierce election year. Jefferson and House leaders lost their first round in district court, but then hailed their appellate victory.

In early June, Jefferson was indicted on 16 bribery and corruption charges related to business dealings in Africa.

This time, the Justice Department is taking issue with the most recent decision in the case, arguing that the judges’ interpretation of the Speech and Debate clause is overly broad because their view establishes a “novel, absolute ‘non-disclosure privilege’” for legislative material.

The lawyers argued that they were not interested in looking at legislative material and that the search warrant in this case sought only materials “outside the legislative sphere.”

“This unprecedented expansion of the clause has not only delayed the instant investigation…it also threatens to complicate numerous ongoing and future and future investigations by inviting litigation over routine techniques employed by federal agents,” Justice Department lawyers wrote in the filing.