PORTLAND, Maine — An environmental group brought together Maine businesses to urge Republican U.S. Sen. Susan Collins to support a rule limiting power plant emissions, an issue that touches on a rift with her party.

The Natural Resources Council of Maine has been enlisting supporters in the state for weeks and on Friday delivered a memorandum to Collins’ office with 400 signatures, asking the senator — who is in the middle of a re-election campaign — to declare support for the U.S. Environmental Protection Agency’s Clean Power plan before she returns to Washington on Monday.

Kevin Kelley, a spokesman for Collins, wrote in an email the senator is still reviewing the EPA’s plan, which calls for reducing carbon emissions from existing fossil fuel power plants by 30 percent from 2005 by 2030.

“Maine sits at the end of the air-pollution tailpipe and thus is harmed by carbon pollution produced in other states,” Kelley wrote. “Sen. Collins has always supported reducing harmful emissions from coal-fired power plants, which threaten public health and the environment.”

Collins was the only Republican senator to vote against legislation that would impose specific restrictions on the EPA’s ability to regulate carbon emissions, essentially hamstringing the agency’s ability to enact tougher standards. However, she’s the only member of the Maine delegation not to declare support for the EPA’s proposal introduced in June, according to NRCM.

“We’re asking her to continue the courage she showed then,” Dan Amory, president of Maine Conservation Voters, said.

Dylan Voorhees, the clean energy director for NRCM, said he hoped Collins would announce her position on the EPA rules before next week’s return to Congress, where the lobbyists for power plants affected by the proposal are more abundant and active.

Voorhees echoed Kelley’s statement that Maine bears the brunt of air pollution from coal-fired plants in other parts of the country and the region should generally support the limits. On top of that, EPA leaders have cited New England’s Regional Greenhouse Gas Initiative, a regional cap-and-trade program for carbon emissions, as a model.

The plan as proposed would affect only four Maine power plants, which would need to reduce emissions by a collective 13.5 percent. Coal is not used at any of the affected Maine plants, which are Wyman Generating Station on Cousins Island in Yarmouth, Maine Independence Station in Veazie, Rumford Power in Rumford and Westbrook Energy Center in Westbrook, according to the Maine Department of Environmental Protection.

Ted Reiner, a former lobster fisherman from Cliff Island, said tougher national power plant emissions standards are an important effort to battling climate change, which has economic consequences for Maine’s nearly $400 million-a-year lobster industry and other fisheries.

The Gulf of Maine has been particularly affected by climate change. The Associated Press reported this week that the waters off Maine’s coast are warming faster than 99 percent of the world’s oceans, which has an impact on fisheries and the rest of Maine’s natural environment, a draw for tourists to the state.

Taryn Hallweaver, a campaign director with Environment Maine, said the proposed power plant emission reductions from the EPA would have the same effect as taking about two-thirds of the country’s gasoline-powered cars off the road.

While the group that included wind industry supporters met outside Collins’ Portland office, the senator was in Castine, visiting the University of Maine’s floating offshore wind turbine project.

Paul Williamson, head of the Maine Ocean and Wind Industry Initiative, said the EPA’s plan would be a boon for the industry.

“The plan supports projects like VolturnUS and other activities like that in Maine,” Williamson said.

The group reiterated expected health impacts of the EPA rules as well.

The EPA estimates the plan will lead to $90 billion in health benefits — preventing up to 150,000 asthma attacks in children and 6,600 premature deaths — based on expected improvements in air quality.

While the plan will be considered by Congress before November, Collins’ stance on environmental issues has become a point of contention in her re-election bid, facing Democratic challenger Shenna Bellows, who has stated support for the proposed EPA rules.