The Supreme Court today ruled against the Environmental Protection Agency’s Mercury and Air Toxics Standard, arguing that the agency did not reasonably consider the regulation’s costs. The standard was developed in 2011 to regulate hazardous air pollutants, such as mercury and arsenic, emitted from 600 plants powered by coal and oil energy sources operating in more than 40 states.

In the 5-4 ruling, EPA was said to have unreasonably interpreted provisions of the Clean Air Act under which this standard was to stand. According to the court, cost should have been a key consideration before determining whether the regulation was appropriate and necessary to implement.

“It is not rational, never mind ‘appropriate,’ to impose billions of dollars in economic costs in return for a few dollars in health or environmental benefits,” Justice Antonin Scalia said.

EPA shared its disappointment with the ruling in a statement released today, but maintained, “this rule was issued more than three years ago, investments have been made and most plants are already well on their way to making emissions reductions.”

According to EPA, the value of the improvements on air quality would have totaled $37 billion-$90 billion each year. In addition, it would prevent up to 11,000 premature deaths, 4,700 heart attacks and 130,000 asthma attacks annually. In 2012, the American Public Health Association filed a motion along with five other health groups, in support of the standard, noting power plants as a key contributor of harmful pollutants damaging to the public’s health.

“This decision will assuredly slow down great progress we’ve made in reducing illness and improving the health of hundreds of thousands of children and adults in just a few years,” Georges Benjamin, MD, executive director of APHA said. “By blocking these standards, our nation’s health pays the ultimate price.”

This ruling takes place prior to an additional set of climate change rules expected to be released by EPA later this summer.