Leaders from a coalition of eastern states, including New Hampshire, have been working for over a year to develop a regional “cap-and-invest” program to reduce carbon pollution from cars and trucks and generate the resources needed to expand clean transit options and improve public health. But Gov. Chris Sununu will no longer be one of them.

The effort, known as the Transportation Climate Initiative began to splinter Tuesday in light of the newly forecast economic impacts, with Sununu announcing that his state would not participate.

“We are already taking substantial steps to curb our carbon emissions, & this initiative, if enacted, would institute a new gas tax by up to 17 cents per gallon while only achieving minimal results. This program is a financial boondoggle and the people of NH will never support it,” he wrote on Twitter.

Money from the program could have been used to pay for a proposed commuter rail link between Manchester, Nashua and Boston that could have significant economic benefits for the state.

The plan to reduce carbon emissions from vehicles by 25 percent would add an estimated 17 cents to the price of a gallon of gas at the pump starting in 2022. If states elected for a smaller reduction goal of 22 percent, the cost per gallon, based on the group’s modeling, would drop to 9 cents.

The third option presented is for a 20 percent emission reduction by 2032 at a cost to drivers of 5 cents per gallon.

The cap-and-invest program is modeled off the Regional Greenhouse Gas Initiative, which focused on driving down emissions from power plants

In addition to Sununu, Vermont’s Republican Gov. Phil Scott has also expressed reservations about joining the pact, although not all 13 states involved need to take part for it to work.

The coalition has estimated $10 billion in public health benefits through the program from reduced cases of conditions like asthma, between 1,900 and 8,900 new jobs and $892 in avoided costs due to climate change.