New England's six governors stepped into uncharted territory Thursday, asking the region's electric grid to help pay for new natural gas pipelines to ease supply constraints.

The governors announced a pact in December to push for regional investment in natural gas pipelines, and the request, in a letter to grid operator ISO New England, marked the first coordinated effort.

Currently, New England electricity customers pay a winter premium for power because the region lacks adequate pipeline capacity for power plants. That situation contributed to the Jan. 1 hike in electric bills, and on Thursday pushed wholesale electricity markets above $400 a megawatt hour, while normal days average closer to $60.

Under the plan, ISO New England would raise money for the pipelines by levying an additional fee on power plants, which would then pass the cost along to customers in their prices. The idea is to jumpstart construction of pipelines because, the governors say, the gas industry isn't moving quickly enough.

"That would be breaking new ground," said Katie Dykes, deputy energy commissioner at the Connecticut Department of Energy and Environmental Protection, who signed the letter to the power grid on behalf of Gov. Dannel P. Malloy.

But it's reasonable, she and other policymakers say. "There is clear interdependency of the reliability of electric system and capacity in the gas system."

With more than half the region's power coming from natural gas-fired plants, the investment through electric bills is warranted and promises savings, supporters say.

"Electricity ratepayers stand to benefit tremendously," Dykes said. "They are paying a price for inaction."

ISO New England backed the plan but one private advocacy group, Environment Northeast, warned that the cost will stick with ratepayers for decades.

Abigail Walker Anthony, director of Environment Northeast's grid modernization and utility reform project, advised "caution when considering those investments in natural gas infrastructure that will take decades to break even — well beyond the time frame of natural gas as a bridge fuel."

"We are recommending a thorough consideration of all alternative approaches … so that consumers are not burdened with overpaying for long-term natural gas infrastructure investments that preclude lower cost and cleaner energy sources," Anthony said in an email.

At least three gas pipeline companies have proposed plans to expand capacity into New England, through either widening pipelines or constructing new lines. Pipeline developers, however, usually wait to build until they have firm commitments to sell the gas to power plants or residential customers, which officials say has slowed the process.

The governors propose to build gas pipelines directly, adding 1 billion cubic feet a day, or at least 600 million cubic feet a day in addition to pending expansion plans. The region's pipeline capacity is currently about 5.6 billion cubic feet a day, according to a 2012 study by engineering consultants, Black & Veatch.

The letter, from a group working with the governors called the New England States Committee on Electricity, also proposed plans to build one or more electric transmission lines that would be able to deliver as much as 3,600 megawatts of clean energy into the region. At a busy time, the 6-state region uses about 20,000 megawatts, and even more on midsummer weekdays.

The gas lines proposal was greeted warmly by ISO New England, which operates the region's wholesale electricity markets in addition to coordinating the grid.

"This would be a novel approach to spurring investment in natural gas pipeline," said spokeswoman Marcia Blomberg, in a written statement. "It is a mechanism that could break the logjam that has stymied the level of natural gas pipeline expansion needed to meet the region's needs."

The tariff would need to go through a stakeholder process and submitted to the Federal Energy Regulatory Commission. ISO New England would be "pleased to contribute to any efforts that will address the urgent need for new natural gas pipelines into New England," Blomberg said.