Allen was the star witness in Kohring's 2007 trial, as he was in the trials of former House Speaker Pete Kott and former U.S. Sen. Ted Stevens.
But revelations about Allen -- that his recollection of events changed over time and that he had sex with minors and tried to cover it up -- have since damaged his credibility.
Until Friday, prosecutors hadn't decided whether they would call him at all. In the notice they filed Friday afternoon saying he would be a witness, they left open the possibility they might still change their mind.
Allen is serving the last two months of a three-year sentence at a halfway house in New Mexico for bribing officials and conspiracy.
Kohring had already decided to call Allen as a witness after his attorneys discovered information in FBI files that showed Allen didn't initially consider some of his payments to Kohring as bribes.
Prosecutors said in their filing Friday they hope to get a court order barring defense attorneys from asking Allen to testify about his sexual relationships with minors, saying it wasn't relevant to the issues in Kohring's trial.
Kohring and Kott are being retried after partial victories in their appeals.
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