Former U.S. Sen. John Edwards is accused of using campaign money to support his mistress, Rielle Hunter.

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NEW: Federal judge tells attorneys to expect ex-mistress to testify for government

Rielle Hunter is the ex-mistress of 2008 Democratic presidential candidate John Edwards

Edwards' upcoming criminal trial will look at whether campaign money went to her

Edwards denies any wrongdoing

CNN  — 

The former mistress of 2008 Democratic presidential candidate John Edwards is expected to be a prosecution witness in his federal criminal trial next month, a federal judge said in court Thursday.

At issue in the approaching North Carolina trial is whether money given to support Edwards’ mistress, Rielle Hunter, by the then-candidate’s benefactors should have been considered donations toward his presidential campaign.

Edwards maintains the money was a gift.

Edwards is charged with six felony and misdemeanor counts related to donations to and payments from his failed 2008 campaign. He is accused of conspiracy, issuing false statements and violating campaign contribution laws. He denies any wrongdoing.

In federal court in Greensboro, North Carolina, on Thursday, Judge Catherine Eagles said that attorneys in the case should expect Hunter to testify on behalf of the government.

If convicted on all counts, Edwards could face 30 years in prison and a fine of up to $1.5 million.

His attorneys have claimed the investigation and prosecution are politically motivated, and the charges do not clearly establish any violation of election law.

His lawyers have argued in federal court the money was a gift unrelated to campaign expenditures and that legally, donors can help pay for a candidate’s personal expenses unrelated to the campaign, according to a report by CNN affiliate WTVD in Raleigh, North Carolina, last October.

The attorneys also said money from donors never went directly to Edwards, but was handled through third parties, WTVD said.

Edwards was Sen. John Kerry’s running mate on the 2004 Democratic presidential ticket.

CNN’s Joe Sutton contributed to this report.