Assistant U.S. Attorney Patricia Gaedeke wrote in documents filed with the 6th U.S. Circuit Court of Appeals that Conyers hasn't offered a plausible explanation for her about-face, the Detroit Free Press reported Wednesday.
Gaedeke said Conyers waited eight months until her sentencing hearing to try to take back the plea.
Conyers argued in her request a lower federal court wrongfully and repeatedly denied her the opportunity to withdraw the plea that landed her at a federal prison camp in West Virginia for 37 months.
She pleaded guilty to accepting bribes in exchange for voting in favor of a $1.2 billion sludge deal.
Conyers is the wife of U.S. Rep. John Conyers, D-Mich.