The Supreme Court announced yesterday it will consider whether the Environmental Protection Agency should have considered the economic expense while adopting its mercury-emissions rule, which utility companies claim carries a compliance cost of around $9.6 billion each year.

Meanwhile, the Obama administration proposed today to impose even more stringent anti-smog regulations, seeking to lower ground-level ozone to between 65 and 70 parts per billion (ppb), down from the current 75 ppb standard.

These two developments are part of a bigger tug of war over the Obama administration’s ambitious environmental agenda, with Republican lawmakers seeking to counter EPA activism.

The Supreme Court ruling could impact the proposed carbon-emissions regulations, too, estimated to cost as much as $73 billion each year. Even by the EPA’s estimates, the rules could carry costs equivalent to all other Clean Air Act rules promulgated up through 2010 combined.

But as the Wall Street Journal reports, the Supreme Court has generally sided with the EPA:

The high court, in its 2007 ruling, allowed the agency to regulate carbon dioxide and other gases associated with climate change. This June, the court said the EPA overreached in claiming the authority to impose greenhouse-gas controls on small emitters, but it said the agency could require controls at power plants and other large pollution sources.

In another case this year, the Obama administration scored a notable victory when the justices revived an EPA program that sought to limit power-plant emissions blowing across state lines, called the cross-state air pollution rule.

The administration also won an important court victory in April when a divided U.S. Court of Appeals for the District of Columbia Circuit upheld the mercury rules, saying the agency acted reasonably in crafting them.

 — Jillian Kay Melchior writes for National Review as a Thomas L. Rhodes Fellow for the Franklin Center. She is also a senior fellow at the Independent Women’s Forum.