Criticizing Pennsylvania power plant operations for carbon emissions, environmentalists are calling for more stringent regulations.

The commonwealth has the third-highest carbon dioxide pollution from power plants in the country, according to a PennEnvironment report based on data collected by the federal government.

Such facilities are the nation's largest source of carbon pollution, said Lina Blount of PennEnvironment.

"In a major step, the EPA is expected to propose an updated rule for cutting carbon pollution for new power plants on Sept. 20," she said Tuesday.

PennEnvironment expects the federal Environmental Protection Agency to issue proposed updated regulations to deal with existing power plants' carbon pollution next summer.

The report lists seven Pennsylvania coal-fired power plants among the top 100 "most-polluting" in the country, based on carbon emissions.

The PPL Brunner Island plant in York County is on the list. A spokesman says the facility has invested more than $860 million in reducing its environmental impact, but the technology doesn't exist yet to reduce carbon emissions without cutting electricity generation.