The link between the coal industry's most influential Washington advocacy group and forged letters sent to members of Congress may be more than a temporary embarrassment for the industry if environmentalists and their allies have anything to do with it.

Left-leaning groups are hoping the scandal will fuel a fall push for getting climate change legislation passed in the Senate.

The letter, they say, bolsters one of their favorite talking points on energy: that opposition to climate legislation comes primarily from a few corporate interests that have little support from the general public.

"I think it's going to have a pretty big impact," said Josh Dorner of the Sierra Club. "I think it shows that opponents of this clean energy legislation will do or say literally anything, even if it means fraud, to try to kill this plan."

At issue are a dozen forged letters sent to three Democratic lawmakers urging them to vote against the comprehensive House energy and climate bill. The letters were tailored to appear as if they came from advocacy organizations in the lawmakers' districts, but they were traced to a lobbying firm, Bonner & Associates.

That firm was working on behalf of the American Coalition for Clean Coal Electricity (ACCCE), which represents major utilities and coal interests.

ACCCE has said the letters were sent by a lone Bonner employee who has since been fired and that the group knew nothing about the letters until after they had been sent. And while ACCCE officials say they are taking steps to address the issue, they do not see it affecting the overall climate debate.

"The reality is, this [is] a very political debate, and every time there's an issue like this, people will want to lose it to score political points," ACCCE spokesman Joe Lucas said.

The Sierra Club has perhaps been the leading group in trying to keep the letters issue alive, running ads in Washington publications and asking the Justice Department to investigate. But the Sierra Club is not alone in the effort. A number of popular left-wing blogs have repeatedly posted on the issue, and it has been discussed several times on MSNBC's "Rachel Maddow Show."

Also, Rep. Ed Markey of Massachusetts, chairman of the Select Committee on Energy Independence and Global Warming and a co-author of the climate bill with fellow Democrat Henry Waxman of California, appears intent on pursuing an investigation into the forged letters.

Markey has sent letters to both ACCCE and Bonner & Associates asking a series of questions about not only the forged letters but also the full extent of the groups' "grass roots" lobbying operations. The lawmaker has asked for a response from the two organizations by this week.

Environmentalists say they expect more revelations of what they see as "dirty" industry tactics, whether related to ACCCE or other critics of the climate bill. "It's difficult to imagine that across the whole range of these groups that are involved in these kinds of tactics that there wouldn't more things like this to come," Dorner said.

Already, some on the left have used the forged letters to dredge up past accusations against Bonner and other groups involved in energy lobbying of questionable tactics used in previous outreach campaigns.

But Lucas said such efforts are unlikely to resonate beyond a sliver of activists already lined up against the group, arguing that left-leaning groups are trying to distract the public from the actual climate debate.

"If one want to, one could choose any grass-roots advocacy program out there, and if you don't agree with them on an issue, you could find fault with something that they do," Lucas said. "The people who care most about this, it is the environmental special-interest groups who are wanting to make an issue of this at this point in time ... because they want to avoid the discussion of what we're talking about in this debate."

'Grass roots' campaigns proliferate

One thing is certain: The scandal has not tamped down grass-roots lobbying operations.

Groups on both sides of the energy debate are using the August recess to try to build public support for their views. Just days after ACCCE revealed its link to the letters, it launched a new project, "America's Power Army," which the group says will use more than 200,000 volunteers to visit town hall meetings and various other events with members of Congress.

"Are we going to continue to do this? Yes we are," Lucas said. "We are going to continue in grass-roots advocacy because this is an important issue and timing is of the essence."

A leading advocacy group for the oil industry will launch its own grass-roots campaign this week, and environmentalists likewise intend to use August to reach out to voters and lawmakers (see related story).

The letters controversy, however, has taken place in an environment where grass-roots tactics as a whole have become a subject of major controversy, though it has little to do with the issue of climate change.

The rallies and town halls that in the past have received little media or public attention are now in the spotlight, as several have been characterized by loud confrontations between attendants and members of Congress.

A handful of conservative advocacy groups have urged their supporters to attend town halls and have provided talking points on speaking to lawmakers. That has created pushback from Democrats, who argue that the furor at many town halls is part of an orchestrated campaign aimed specifically at defeating the White House's agenda on health care, climate and other issues.

Dorner of the Sierra Club said controversies around the town halls have helped make the case that similar tactics were used in the climate debate.

"We've seen all the activity around these town halls," Dorner said. "That same level of vitriol and activity happened over e-mail and the phone after the energy bill vote."

If nothing else, some environmentalists say, the controversy certainly creates the perception that critics of the legislation have little merit behind their arguments.

"No one thing ultimately decides this issue, but this can only hurt opponents of action in the Senate, because it makes it appear that they're desperate," said Frank O'Donnell of Clean Air Watch. "You have to wonder, if their argument is so sound, why such deception?"

That line of thinking goes to the heart of what environmentalists see as another potential fallout from the forged letters -- a public questioning of the foundation of industry arguments.

Dueling economic reports

The climate debate has featured dueling reports on the predicted economic and environmental impacts of cap-and-trade legislation. Politicians and advocacy groups pounce on reports that line up with their positions and try to shoot down those that run contrary.

But O'Donnell of Clean Air Watch said that, in light of the controversy, the public and some on-the-fence lawmakers are likely to take a more skeptical view of any such analysis from industry groups and their supporters. He said he expects the issue to be raised in the congressional debate as lawmakers spar over the anticipated consequences of the legislation.

"I would not be surprised if, when it comes to debate, that this is going to be brought forward, because a lot of this is going to be about credibility -- whose numbers do you believe and whose projections do you believe," he said. "I certainly think it could taint some of the other corporate arguments on this issue."

Critics of cap-and-trade legislation, however, dismiss such arguments, claiming that environmentalists themselves use misleading and inaccurate data to make their case with seemingly little fear of political repercussions.

"I don't think the greens have a materially better case than before, now that the other guy has been caught dipping his toe in a pool of misleading claims or tactics, which they're up to their neck in," said Chris Horner of the Competitive Enterprise Institute.

And Horner dismissed the idea that the controversy will affect votes on Capitol Hill. He said, "I see very few members open to substantive persuasion, with the fence-sitters making wholly political calculations: How does this impact my numbers at home and whatever future plans I might be considering?"