MERRILLVILLE - The Indiana Utility Regulatory Commission has approved an electric rate increase for Northern Indiana Power Supply Co, a subsidiary of Merrillville-based NiSource (NYSE: NI). The utility says the hike will cause the average residential customer’s electric bill to go up about $6 per month.

NIPSCO says the new rates will go into effect in two phases, the first on January 1 and the second on March 1

The utility had originally requested an increase of about $11 to its customers throughout northern Indiana. NIPSCO is hiking the customer bills to help pay for upgrades to the electric infrastructure and to pay for what the company calls environmental upgrades.

The utility is retiring its coal-fired generation plans and shifting towards more renewable sources, such as wind power.

In addition to the usage rate increase, the IURC order reduced the monthly fixed charge for residential customers by 50 cents to $13.50. NIPSCO had originally requested an increase of that fee to $17.