At issue is the Constitution's speech and debate clause.  Rep. Jefferson thinks it applies to the testimony of his staff at the grand jury.  The judge ruled against him, hence the appeal, which will delay the start of the criminal trial:

U.S. Rep. William Jefferson, D-New Orleans, on Wednesday afternoon appealed a court ruling in his public corruption case, a move that is sure to once again put off the twice-delayed trial.

Jefferson is challenging the refusal by U.S. Judge T.S. Ellis III to dismiss numerous bribery-related charges because the Grand Jury that indicted him last June, he contends, heard tainted testimony about his legislative activities in violation of the U.S. Constitution.

Jefferson 's trial, originally scheduled for Jan. 16, was slated to open Feb. 25. But proceedings will be put on hold while a three-judge panel of the Fourth Circuit Court of Appeals considers Jefferson's arguments, which could take months, legal experts say. Whoever loses at the appellate court is likely to take the matter to the U.S. Supreme Court, further delaying the much-anticipated trial of the nine-term congressman.