MERRILLVILLE, Ind. — Northern Indiana Public Service Co. says it has asked state regulators for an increase in its base rates for natural gas.

The Merrillville-based utility serving gas 820,000 customers in 32 counties says it has proposed an increase that would be phased in in mid-2018 and fully implemented by early 2019. If approved, the full increase would cost customers $143.5 million annually. Any increase would need approval from the Indiana Utility Regulatory Commission.

NIPSCO says residential customers using 69 therms per month and paying $50 now would see an overall increase of $10 per month.

The company says its base natural gas rates haven’t increased in more than 25 years and a regulatory review led to a slight decrease in 2010.

Customers will have opportunities for public comment on the request.