Attorney General Cuomo, subpoenaed five power companies to determine whether they disclosed to investors enough information about the financial risks of using coal to generate electricity.

AES Corp., Dominion Resources Inc., Dynegy Inc., Peabody Energy Corp., and Xcel Energy Inc. received letters noting carbon dioxide emissions from coal-fired plants have been linked to global climate change and are likely to be subject to future regulation.

“Regulation of greenhouse gas emissions on the state level, such as through the Regional Greenhouse Gas Initiative, will begin shortly in several states,” the September 14 letters to each company say. “Such regulation would likely add a significant cost to carbon-intensive coal generation.”

“A public company must disclose information material to a shareholder’s investment decision,” the letters state.

Each letter says the attorney general’s office is “concerned” that the companies have “failed to disclose material information about the increased climate risks” each business faces, or the “possible effects of future greenhouse gas regulations” and their potential impact on the companies.

Mr. Cuomo’s letters invoke New York’s Martin Act, a state securities law that gives broad powers to state prosecutors. Governor Spitzer used them while attorney general to probe allegations of Wall Street misconduct. The letters ask for a response by October 9, 2007.

Xcel said in an e-mailed statement to Bloomberg News that it is building a Colorado plant under a deal with environmental groups. “Our financial disclosures are adequate. We look forward to discussing this matter further with the New York attorney general,” the company said in the e-mail sent by a spokesman, Thomas Hoen.

A spokesman for Dominion, Richard Zuercher, a spokeswoman for AES, Robin Pence, and a Dynegy spokesman, David Byford, declined to comment. A spokesman for Peabody Energy couldn’t be reached for comment.

The cost of generating power at American coal-fired plants during the second quarter of 2007 was about 43% less than the most efficient natural gas-burning plants, a coal analyst for Natixis Bleichroeder in New York, Jeremy Sussman, said.

In March, a Massachusetts Institute of Technology study reported that coal gasification may not be the best option for companies to use as fuel in power plants, citing its potential environmental costs.