The Legislature passed the Illinois Clean Coal Portfolio Standard in 2008, requiring utilities and other power suppliers to purchase 5 percent of their electricity from coal-fueled plants that capture at least half of the carbon dioxide. The law capped the rate impact from the Taylorville project at 2 percent for residential customers -- a negotiated agreement with the attorney general and the Citizens Utility Board, based in Chicago, to help win support for the project.

But there is no such limit to rate increases for big electricity users such as industrial customers, local governments and schools.

That fact gave rise to a coalition of businesses that's opposing Taylorville. They say the project will increase their rates 3 to 4 percent a year and produce an $8.7 billion subsidy for the project's developers over the next 30 years. The group says the additional electricity costs will produce an unnecessary burden for Illinois employers and kill more jobs than it generates.

"We don't think that's a very good tradeoff," said Dave Vite, president of the Illinois Retail Merchants Association, which represents 23,000 stores across the state. "Jobs will be lost because we won't have the capital to build and operate our businesses."

Developers, led by managing partner Tenaska Inc., an energy firm based in Omaha, Neb., say opponents are distorting the facts. Big electricity consumers will see the same increase as residential customers. But the percentage increase will be larger because industrial customers and manufacturers already pay far lower rates.

The jobs argument is also disingenuous, Tenaska says. There will be no rate impact for at least five years while construction is ongoing, and the project will generate 2,500 construction jobs, plus hundreds of operations, mining and trucking jobs when it's complete, the company says.

The plant is planned for a 713-acre site just northeast of Taylorville, about two hours northeast of St. Louis. The 602-megawatt plant would be large enough to power about 600,000 houses. Unlike the state's other coal-fired plants, it won't burn pulverized coal; it will convert the black rock to a synthetic gas, making it possible to strip out carbon dioxide and other pollutants before combustion.

Tenaska officials have billed Taylorville as the cleanest coal-fueled power plant in the world, capturing nearly two-thirds of its carbon dioxide emissions. The CO2 would be injected thousands of feet below ground into a layer of porous rock or sent via pipeline to the Gulf Coast and used for oil recovery.

Developers have secured a federal $417 million tax credit from stimulus funds and a $2.58 billion federal loan guarantee to help finance the project. But they say the state legislation is still critical.

Taylorville's supporters include Sen. Dick Durbin and the AFL-CIO as well as a couple of unusual allies -- the Illinois Coal Association and American Lung Association of Illinois.

Opponents also include strange bedfellows -- the Sierra Club and the Illinois Chamber of Commerce -- as well as big-business interests such as the Illinois Manufacturers Association, agricultural giant ADM and electric company Exelon.

Both sides have ramped up public relations efforts in recent weeks as the Legislature begins its fall veto session. Legislation to advance the project is expected to be filed just after Thanksgiving.

Bart Ford, Tenaska's vice president of development, said the company had done what was required by the Legislature. It completed engineering work and submitted a detailed cost study to the Illinois Commerce Commission. Now the company must have an answer.

"We definitely do need an answer in the veto session," he said.

The ICC also hired a consultant, at Tenaska's expense, to study cost estimates.

"The (Taylorville Energy Center) features high costs to ratepayers with uncertain future benefits, and uncertainties that potentially add to already-significant costs," the commission said in its report.

Electricity produced at Taylorville would cost 21 cents a kilowatt-hour -- twice as expensive as nuclear or wind power, according to the report. The ICC said the rate impact for residential customers would approach the 2 percent cap, and additional costs or overruns would fall disproportionately on the backs of big electricity users and alternative retail electric suppliers. The commission also raised doubt about whether plant could be complete by 2016.

Whatever the Legislature decides, its action could make or break the Taylorville project, one of the nation's most ambitious attempts to build a cleaner coal-fueled power plant. It could also have meaning for another proposed clean coal plant that will require the legislature's OK.

St. Louis-based Ameren Corp., whose 70-year-old power plant in Meredosia, Ill., would be the centerpiece of the federal government's revamped FutureGen project, has indicated that the project would require legislation to guarantee cost recovery. Ameren will seek legislative approval only if a detailed engineering study shows the project is feasible.

Ameren spokeswoman Susan Gallagher said it was too early to speculate about whether the Taylorville legislation would have an impact on FutureGen.

Doug Whitley, CEO of the Illinois Chamber of Commerce, said a clean-coal project should be able to compete within a competitive electricity market.

"We would like to see clean coal demonstration projects," he said. "But if they're going to be economically viable, they need to stand on their own."

Tenaska's Ford said that view was short-sighted. Up to 40 percent of Illinois' current coal fleet -- dirtier plants that are decades old -- could be shut in coming years as more stringent environmental rules take effect, leaving the state at the mercy of more volatile natural gas prices. "The do-nothing approach in the long run is going to be much more expensive than building clean coal plants now," he said.