In this April 26, 2021, file photo, workers pound stakes to mark land on an existing Central Maine Power power line corridor that has been recently widened to make way for new utility poles near Bingham. Credit: Robert F. Bukaty / AP

AUGUSTA, Maine — Energy companies poured another $23 million into the Central Maine Power Co. corridor fight in the first three weeks of October, bringing total spending over the past two years to more than $87 million ahead of the Nov. 2 referendum.

It highlights the high stakes of the upcoming vote for energy companies on both sides of the issue, as CMP stands to benefit financially from the completion of the corridor project — which would bring hydropower from Canada through western Maine to connect with New England’s energy grid in Lewiston, while rival energy companies would lose market share.

The money that has flown into the race in the past three weeks alone would have been enough to make it the most expensive referendum campaign in Maine’s history. It is also the second-most expensive Maine political race ever, trailing only last year’s U.S. Senate race between Sen. Susan Collins and her unsuccessful Democratic challenger Sara Gideon.

CMP and its affiliates continue to be the largest spender in the race, adding more than $8.6 million between Oct. 1 and Oct. 24, according to data reported to Maine’s campaign finance regulator. In total, CMP and related companies have contributed more than $42 million to political groups since the fall of 2019.

NextEra Energy, which operates the oil-powered Wyman Station in Yarmouth along with the nuclear-powered Seabrook Station in New Hampshire, gave another $6.5 million during the first three weeks of October to Mainers for Local Power, the largest anti-corridor group.

That brings NextEra’s total political spending to more than $20 million, with the Florida-based energy company surpassing Hydro-Quebec, the Canadian energy company that would supply hydropower for the corridor, to become the second-largest overall spender in the race. Two other energy companies opposing the corridor, Vistra and Calpine, gave another combined $3 million to Mainers for Local Power as well.

Hydro-Quebec also added another $5 million to its own political committee since the start of October, bringing its total political spending to $19.8 million. Each of the major groups funded by the five energy companies dedicated the majority of its spending to ads in the past few weeks.

The corridor fight has dominated the airwaves in the lead-up to the Nov. 2 election, with CMP and its allies highlighting the retroactive portions of the referendum and, to a lesser extent, pointing to economic and clean energy benefits of the corridor project itself, while opponents of the project focus on distrust of the utility company and concerns about the environmental impacts of construction.