Duke Energy Corp. and consumer groups will revise an agreement on how to pay for higher-than-expected construction costs at an Indiana power plant.

Dand the groups said in a statement.

Duke, the biggest power supplier in Indiana, raised the estimated price of the plant, being built near Vincennes, to $2.88 billion in April.

The “integrity of the process” has been called into question by recent revelations of e-mail exchanges between Duke Energy and David Lott Hardy, the former head of the Indiana Utility Regulatory Commission, Indiana Utility Consumer Counselor David Stippler said in the Duke statement.

On Dec. 6, Duke’s top utility executive, James L. Turner, 51, resigned due to concerns about e-mail exchanges with Hardy.

E-mails obtained under an open records request by the Indianapolis Star showed Turner and Hardy discussing personnel matters and personal topics and “sometimes trading messages eight or 10 times day,” according to a Nov. 28 article in the newspaper.

Indiana Governor Mitch Daniels fired Hardy because he allowed Scott Storms, a former administrative law judge for the Indiana Utility Regulatory Commission, to preside over cases involving Duke Energy while Storms was discussing a job with the company, the governor’s office said in October.

Hardy, reached by telephone, declined to comment.