Rep. Ed Markey (D-Mass.), chairman of the Energy Independence and Global Warming Committee and a co-author of the cap-and-trade bill, has called an investigative hearing Thursday morning on forged letters sent to Congress on behalf of the American Coalition for Clean Coal Electricity.

The hearing, which will focus on the forged letters, will also more broadly address the practice of AstroTurf, which refers to paid grass-roots efforts.

Markey spokesman Eben Burnham-Snyder declined to name the witnesses, saying it was the committee’s policy not to release the names until they had been confirmed. The witnesses will be “principal players— in the scandal, according to Burnham-Snyder.

Markey opened an investigation into the letters this summer.

A temporary employee of Bonner & Associates allegedly falsified the letters on behalf of ACCCE.

The correspondence was sent to Democratic Reps. Tom Perriello (Va.), Kathy Dahlkemper (Pa.) and Christopher Carney (Pa.) before the House’s June 25 vote on the bill.

The forged letters were made to look as if they had come from a Charlottesville, Va., NAACP chapter, the Hispanic advocacy organization Creciendo Juntos, the Jefferson Area Board for Aging, the nonprofit Erie Center on Health & Aging and the American Association of University Women.