And these new letters plumb the depths of sleaziness.

The letters, written under the names of local senior centers, urged Reps. Kathy Dahlkemper (D-PA), Christopher Carney (D-PA), and Tom Perriello (D-VA), to make changes in the Waxman-Markey climate change bill because fixed-income seniors were worried about energy price hikes.

As a letter to Dahlkemper, purportedly from Slippery Rock Senior Center in Slippery Rock, PA, put it:

Many of our seniors, as you know, are on low fixed incomes. Some of our seniors have even received decreases to their social security payments. Further making it a difficult choice to meet the basic necessities of life (food, prescription medication and the like). The cost to heat and cool their homes, run hot water and use othe appliances is very important to those seniors on a budget.

Our state gets 56% of its electricity from coal. We urge you to pass legislation that reduces greenhouse gases but at the same time protects seniors and consumers from unaffordable increases in the basic necessity of electricity.

Of course, the letter wasn't crafted by concerned advocates of seniors at all -- but by skilled Washington astrotruf lobbyists.

Read two other letters to Dahlkemper here and here. The letter to Carney is here, and to Perriello here. They all follow the same script.

Rep. Ed Markey's Select Committee on Energy Independence and Global Warming, which is investigating the matter, now puts the number of confirmed forged letters at 13.

Markey is calling on Bonner & Associates as well as coal industry group American Coalition for Clean Coal Electricity -- for whom Bonner was working, through an intermediary firm -- to verify whether dozens of other letters are real or fake. 58 letters were sent in all, according to the committee.