The Environmental Protection Agency is warning states that the federal government is ready to impose smog rules on them if they don't comply on their own.

The agency updated its once-embattled Cross-State Air Pollution Rule, which seeks to curb downwind pollution from one state to another. The rules when issued were considered a threat to power plants, forcing many companies to shutter plants or curtail operations. The rules went through a rigorous court fight, in which EPA ultimately won.

Tuesday's updates would "reduce summertime emissions of oxides of nitrogen (NOx) from power plants that contribute to downwind ozone problems" in the eastern half of the U.S., the EPA said.

The updated rule will cost states $23 million a year beginning in 2017, the agency said, arguing that the rule's benefits of between $700 million and $1.2 billion greatly outweigh the cost.

Read more on WashingtonExaminer.com