Sandlin, 56, of Sherman, Texas, was released without bail after his arraignment in U.S. District Court in Tucson. He and his lawyer declined to comment.
Renzi pleaded not guilty to the charges on Tuesday. Both are due back in court April 29.
The indictment accuses Renzi of telling groups seeking to get the surface rights to an Arizona copper deposit that they would have to buy land owned by Sandlin to win required congressional approval for the land exchange.
After an investment group agreed to buy the land, Renzi received $733,000 from Sandlin, the indictment said. Sandlin had owed Renzi money from a previous land deal.
Renzi and another co-defendant are also charged with eight other counts.
Renzi will stay in office, his lawyer Reid Weingarten said. Renzi, a three-term Republican whose 1st Congressional District covers most of northeastern Arizona, announced last year that he would not seek re-election.