(Greensboro, NC) -- The judge overseeing the criminal trial of John Edwards will sharply curtail the testimony of a key witness for the defense as they try to prove he didn't break the law.

Edwards' lawyers had intended to call former Federal Election Commission chairman Scott Thomas as their first witness Monday morning, but prosecutors objected.

The jury left the room while Judge Catherine C. Eagles listened to his testimony.

Thomas said it was his opinion that nearly $1 million secretly used to hide Edwards' pregnant mistress as he campaigned for the White House did not qualify as campaign contributions under federal law.

The judge ruled that Thomas won't be allowed to say that in front of the jury.

Edwards has pleaded not guilty to six criminal counts related to campaign finance violations.