Pennsylvania American water and wastewater customers would see their monthly bills increase about 25% next year under a $173.2 million rate increase request, which state regulators on Thursday agreed to examine more closely in a series of hearings.

The Pennsylvania Public Utility Commission on Thursday voted 3-0 to formally investigate the rate request by Pennsylvania’s largest private water company. The rate request, which was filed April 29, has already attracted an outpouring of opposition to the regulatory agency.

Pennsylvania American serves about 400 communities across the state, including clusters of water customers in Bucks, Montgomery and Chester Counties anchored around such towns as Norristown, Coatesville and Yardley.

Investigations of rate requests are routine and give the PUC nine months from the filing date to make a decision.