Four days of intensive hearings will begin tomorrow morning to discuss a draft of “The American Clean Energy and Security Act of 2009” which one participant calls the most important piece of energy legislation in the last 50 years.

The bill is authored by House Energy and Commerce Committee Chairman Henry Waxman and Subcommittee on Energy and Environment Chairman Ed.

Over 50 groups have been called to testify including the head of the Department of Energy, the Department of Transportation and the Environmental Protection Agency, as well as company representatives from Duke Energy Inc., Alcoa Inc, NRG Energy Inc. , Conoco Phillips, DuPont and Google Inc.

“It is critical that Congress hears a large number of individuals representing different organizations as it looks into changes to make to the bill,” said participant Dian Greunich, Commissioner of the California Public Utilities Commission.

This bill will be the most significant energy and climate legislation that the United States has ever enacted, the most important piece in probably 50 years, Greunich said in an interview on Monday.

The 648-page bill aims to cut greenhouse gases 20 percent by 2020 and proposes new energy efficiency standards and a cap-and-trade system for the United States. It is expected to clear the house before August, Waxman has previously said. The U.S. Congress will pass the bill as soon as this year, White House Chief of Staff Rahm Emanuel told ABC yesterday.

Topics for discussion during the hearings include the bill's agenda for green jobs and economic benefits, policies for consumers, U.S. competitiveness and International participation as well as carbon capture and storage, renewables, grid modernization, carbon electricity, energy efficiency, transportation, building appliances utilities and the carbon market, among many others.