Stevens' defense lawyers disclosed the allegation in a motion asking permission to quiz the witness, David Anderson, and to schedule a hearing to consider a letter Anderson wrote to U.S. District Judge Emmet Sullivan, who presided in the case, The Washington Post (NYSE:WPO) reported.

In the filing, the attorneys accused federal lawyers of "suborning perjury and making intentionally false statements" tied to the witness's testimony.

In the letter Anderson said he also believed he had an agreement of immunity from the prosecution but during the trial he testified that there was no deal.

Stevens was convicted in October on seven felony counts of failing to disclose $250,000 in gifts and home renovations on Senate financial disclosure forms. Federal prosecutors accused Stevens of accepting many of the gifts and renovations from the oil services firm Veco and its top executive, Bill Allen, a close friend of Stevens'. Anderson is Allen's nephew, lives in Alaska and worked for Veco.

"Without the preparation from the prosecution and the reminders from them about my activities and the agreement I had with them about my family and myself," he wrote, "I would not have given the same testimony."

Justice Department spokeswoman Laura Sweeney told the Post the department wouldn't comment.