Tomorrow, the U.S. Senate will take up a controversial measure that would restrict the ability of the U.S. Environmental Protection Agency to control the release of greenhouse gases by cars and industry. Maine's two moderate Republican senators are considered swing votes on Alaska Senator Lisa Murkowski's resolution. Both Maine Sens. Susan Collins and Olympia Snowe have been critical of EPA rules and won't say how they will vote, which is unsettling to environmental groups and state officials.

"The Senate should defeat it and act swiftly to lessen the extensive damage caused in the Gulf, to cut our oil dependence and move to a clean energy economy," says Paul Burns, who is with the group Environment Maine. He says the resolution detracts from the climate change legislation currently pending in Congress, including a bill sponsored by Sen. Collins.

"EPA would have to rescind its clean car standards because the resolution would veto EPA's scientific findings that global warming pollutants endanger human health and the environment," Burns says.

A sticking point for Collins does not have to do with car emissions but the way EPA intends to regulate emissions from burning biomass -- which is to say, no differently from other sources of greenhouse gases.

The forest products industry maintains that biomass users should be exempted from EPA rules. They consider biomass combustion carbon-neutral because it releases carbon dioxide into the air, offsetting the CO2 trees sucked in during their growth.

Collins appears to be on the same page. In a statement she says, "While I support regulating greenhouse gas emissions, I have reservations about the sweeping approach EPA is pursuing. For example, for the first time the EPA has classified biomass as not carbon neutral, which could have a negative impact on Maine's forest products industry."?

But Maine Environmental Commissioner David Littell says it's one thing to call biomass harvested from sustainable forests carbon-neutral. But he says not all biomass is the same. "We can't accept the proposition that trees that are harvested and cut down for permanent development ,that never are going to grow back again, is sustainable and carbon-neutral. Obviously those trees are never going to regrow."

Littell has sent a memo to both senators, urging them to reject the Murkowski resolution, which also seeks to undo the EPA's greenhouse gas standards on tailpipes. "This resolution is clearly heavily supported by the petroleum industry and by the coal industry in this country, and it's really about greenhouse gas reduction and whether we're going to clean up our air and clean up the air sources that are upwind of us," Littel says.

Gov. John Baldacci has personally written the senators. David Farmer, a spokesman for the governor, says that passage of the resolution would be a step backward for Maine, which he describes as a national leader on climate change.

"Maine was one of the states that joined Massachusetts in suing the EPA to move forward with the control of greenhouse gases under the Clean Air Act," Farmer says. "Maine is among the 10 states that were part of the regional greenhouse gas initiative, which is one of the first programs in the country to control greenhouse gases."

Collins is not just getting pressure from within Maine. The national advocacy group, Americans United for Change, is also running ads in Maine against the resolution.

The ads specifically target Collins, but spokesman Jeremy Funk says the group would have liked to target Maine Sen. Olympia Snowe as well, whom he says, in recent days, has been rumored to be open to the resolution.

Snowe's office maintains that she is still reviewing the legislation, but points out that the senator is worried about what repercussions the new EPA rules will have for dozens of major employers in Maine.

President Obama has signaled he will veto the Murkowski resolution. But Lisa Pohlmann of the Natural Resources Council of Maine says that this does not give senators a pass to approve the resolution.

"The U.S. is the biggest emitter in the world and we have to be the leaders on taking action by our government," Pohlman says. "We really believe that there's an important window right now for legislation to actually be able to move through the Senate and on thorough Congress, and this is just not the moment to show any weakness, any sense that this is not an important issue."

The Senate is expected to take up the resolution in the morning. The measure needs needs only 51 votes instead of the typical 60 because it falls under a special Congressional procedure for measures that change agency rules.