Republicans and industry groups are sharpening their opposition to proposed Environmental Protection Agency emissions rules for new power plants by saying the agency violated federal law by basing its standard partly on projects that received federal subsidies.

The argument is that the EPA is running afoul of the Energy Policy Act of 2005 by requiring new power plants to install carbon capture and sequestration technology, which traps carbon emissions and stores them underground, because the law forbids rules on projects that receive federal dollars.