Rep. Ed Markey (D-Mass.) has uncovered five more forged letters as part of his investigation into fraudulent correspondence sent by Bonner & Associates on behalf of the American Coalition for Clean Coal Electricity opposing the House climate change bill.

Markey, chairman of the Energy Independence and Global Warming Committee and a co-author of the cap-and-trade bill, on Tuesday released the letters, which were purported to come from senior centers and elderly services organizations.

The additional letters bring the total to 13 forged letters from nine different community groups. The committee received the letters from ACCCE and Bonner & Associates after Markey opened an investigation earlier this month.

“We’ve seen fear-mongering with our nation’s senior citizens with health care, and now we’re seeing fraud-mongering with senior citizens on clean energy,— Markey said in a statement.

In a statement, ACCCE said it is continuing to work with the Select Committee in its investigation into letters sent to Capitol Hill after it subcontracted ACCCE’s grass-roots letter-writing effort to the Hawthorn Group, which later hired Bonner & Associates.

“We are continuing to take all possible steps to determine the authenticity of all letters Bonner and Associates submitted under its limited scope of work with the Hawthorn Group on behalf of ACCCE,— the statement said. The group declined to make any additional details public “out of respect— for the ongoing investigation.

The newly released letters were sent as if they were from groups such as the non-profit Erie Center on Health & Aging.

Earlier forged correspondence was made to look as if it had come from the Charlottesville NAACP Chapter, the Hispanic advocacy organization Creciendo Juntos, the Jefferson Area Board for Aging and the American Association of University Women.

The committee is still verifying dozens of the 58 letters sent to Democratic Reps. Tom Perriello (Va.), Kathy Dahlkemper (Pa.) and Christopher Carney (Pa.) before the House’s June 25 vote on the bill.

All three Members represent conservative, Republican-leaning districts and could be vulnerable in the 2010 elections.