Greensboro, N.C. — Federal prosecutors on Thursday granted John Edwards' former mistress immunity from criminal charges for anything she says on the witness stand during the former Democratic presidential candidate's upcoming trial.

Edwards faces six criminal counts related to alleged campaign finance violations for using nearly $1 million from two wealthy donors to hide Rielle Hunter, who was pregnant with Edwards' child, during his 2008 campaign. He has pleaded not guilty, claiming that the money was a gift and not campaign contributions.

Jury selection is to begin April 12, and prosecutors say it's possible Hunter will be asked to testify.

U.S. District Judge Catherine Eagles ruled Thursday that two of Edwards' attorneys who represented Hunter in a civil suit cannot cross-examine her if prosecutors call her as a witness.

Under the agreement offered by the government, Hunter cannot be held criminally liable for any actions she testifies to as long as she's truthful.

Prosecutors had challenged the addition of Alan Duncan and Allison Van Laningham to Edwards' defense team, alleging a conflict of interest.

The pair represented Hunter in her civil lawsuit against former Edwards aide Andrew Young over items she said Young and his wife took from her, including a purported videotape showing Edwards and Hunter engaged in sex.

Young and Hunter settled the suit last month, and the settlement called for the sex tape to be destroyed.

Both Edwards and Hunter said there would be no conflict of interest, and Eagles said Duncan and Van Laningham could represent Edwards.

The judge also allowed Charlotte attorney Jim Cooney, who has represented Edwards since early in the federal investigation, to withdraw from the case.