Updated at 10:15 a.m. on Aug. 24.

The American Coalition for Clean Coal Electricity said Thursday that it would no longer be working with Bonner & Associates, the grassroots lobbying firm founded by Jack Bonner, whose employee sent false letters to lawmakers urging them to vote against the House energy legislation.

"We will not be working with Mr. Bonner again," Joe Lucas, senior vice president for communications at ACCCE, told NationalJournal.com. "ACCCE did nothing wrong. Looking back, there would be many things we would do differently."

Bonner's firm was hired by ACCCE's subcontractor, the Hawthorn Group. Lucas said his group is in the process of determining exactly what it could have done differently. "We're taking this very seriously, but we do recognize that this was an isolated incident involving the wrongdoing of someone working for a subcontractor."

The Hawthorn Group itself cut ties with Bonner over the fake letters in June, according to ACCCE.

Whether ACCCE will continue to work with Hawthorn is still under review, Lucas said. But his comments suggest the middleman in this scandal is not losing out. "Hawthorn has been a consultant in this area for over 10 years and has a very, very good record of performance," Lucas said. "And this is, again, a very serious but isolated incident."

CLARIFICATION: The original version of this post implied that ACCCE was announcing the firing of Bonner & Associates. A company representative subsequently told us that the subcontractor, the Hawthorn Group, had already fired Bonner in June.