A multibillion dollar clean coal tax credit is being investigated by the U.S. Congress after new evidence has been discovered linking the chemically treated coal to an increase in pollution rather than a decrease.

Over the last decade, America's largest corporations have invested billions of dollars in clean coal technology and the tax credit, which is meant to reduce smog, among other benefits. Companies who have seen a strong return on investment include a who's who of major firms, including Fidelity Investments, Goldman Sachs Group Inc and JPMOrgan Chase.

Last year, according to the U.S. Energy Information Administration, about 150 million tons of coal was burned nationally, according to a Yahoo News investigation.

Nonprofit Resources for the Future spoke with Reuters, confirming that chemically treated coal power plants were not seeing mercury, nitrogen oxide and sulfur dioxide pollution reduced to the volume expected to quality for the subsidy.

The tax credit will expire at the end of the year. Congress has the power to renew it.