The Northern Indiana Public Service Company amended its electric rate case proposal with the Indiana Utility Regulatory Commission on Monday.

Instead of the two rate increases proposed in August, NIPSCO is seeking one base rate increase. All customer rates will increase by an average of 9.8 percent.

For residential customers using an average of 735 kilowatt hours monthly, the bill would increase from $81.68 to $94.44 -- a 15.62 percent increase.

Increases will likely be lower among commercial and industrial customers, due to servicing and transmission costs.

The company changed its filing with the recent addition of the Terre Haute's Sugar Creek electric generating facility which began serving NIPSCO's customers on Dec. 1.

NIPSCO has not sought a base rate increase in more than 20 years. The company said the increased revenue will cover more operating and maintenance costs.

The review process can take 12 to 18 months, and the IURC will determine the new rates which are expected to be effective in late 2009 or early 2010.

Hammond Mayor Tom McDermott Jr. and LaPorte County attorney Shaw Friedman are among the groups that will oppose the proposed rate increase before the IURC at a January hearing.