Sleepy Missouri senators worked through the night into a new day Thursday as a small group of lawmakers filibustered a bill that could reward utilities making improvements to their infrastructure with more consistent rate increases on their customers.

The legislation changing the way investor-owned utilities are regulated drew intense opposition from some senators who said it would drive up costs for millions of residents and businesses. Supporters countered that rates are likely to rise anyway, and the bill would provide predictability by limiting annual average rate increases to 3 percent.

The Senate began debating the bill at around 7 p.m. Wednesday and worked through the night without a break as opponents made scores of quorum calls summoning sleepy senators who had retreated to their offices to return to the chamber.

The opposition was led overnight by Republican Sens. Doug Libla of Poplar Bluff, Gary Romine of Farmington, and Rob Schaaf of St. Joseph. They were joined Thursday morning by Democratic Sen. Maria Chappelle-Nadal, of University City.

"My concerns are that the bill will raise rates on our constituency. It will not only raise rates on the little old lady down the street but businesses and industry across the state that provide jobs for our citizens," Romine said Thursday.

The bill would change the way in which the Missouri Public Service Commission regulates electric and natural gas corporations such as Ameren Corp., Kansas City Power & Light Co., The Empire District Electric Co. and Spire Inc.

Such companies currently work through lengthy rate cases at the PSC, which sets their rate of return on investment.

When utilities make infrastructure improvements between rate cases, the new facilities began depreciating immediately and the full cost of that capital investment is sometimes not fully recovered by utilities in subsequent rate cases, said Warren Wood, Ameren Missouri's vice president of legislative and regulatory affairs. He said the legislation would encourage infrastructure investment by changing the accounting method for those improvements.

"It would benefit our customers with those investments to modernize the grid, and it would allow us to more accurately recover the costs so we could ramp up those investments," Wood said.

Senate Majority Leader Mike Kehoe, a supporter of the bill, said Thursday that he wants to continue pushing toward an eventual vote but has no plans to employ a procedural move to shut off a filibuster and force a vote.

"The current system that we have that's outdated will allow for unpredictable and sometimes uncontrollable rate increases," said Kehoe, a Republican from Jefferson City. The bill "allows the utilities to perform the maintenance and infrastructure improvements they need to do with a predictable rate for both residences and businesses."

Supporters have offered various versions of the legislation this session. The latest version includes a provision giving the PSC the authority to more quickly lower rates for consumers to account for corporate tax cuts included in a new federal tax overhaul. Republican Sen. Ed Emery, of Lamar, said that provision could result in savings of $100 million for consumers.