WASHINGTON (AP) -- The Environmental Protection Agency said Thursday it is delaying planned rules to curb emissions from existing natural gas plants that release harmful air pollutants and contribute to global warming.

The agency said it is still on track to finalize rules for coal-fired power plants and new gas plants that have not come online, a key step to slow planet-warming pollution from the power sector, the nation's second-largest contributor to climate change.

But in a turnaround from previous plans, the agency said it will review standards for existing gas plants and expand the rules to include more pollutants. The change came after complaints from environmental justice groups, who said the earlier plan allowed too much toxic air pollution which disproportionately harms low-income neighborhoods near power plants, refineries and other industrial sites.

"As EPA works towards final standards to cut climate pollution from existing coal and new gas-fired power plants later this spring, the agency is taking a new, comprehensive approach to cover the entire fleet of natural gas-fired turbines, as well as cover more pollutants,'' EPA Administrator Michael Regan said in a statement.

He called the new plan a "stronger, more durable approach" that will achieve greater emissions reductions than the current proposal. It also will better protect vulnerable frontline communities suffering from toxic air pollution caused by power plants and other industrial sites, Regan said.

Still, the plan was not universally welcomed by environmentalists, who the said the new approach will likely push rules for existing gas plants past the November presidential election.

"We are extremely disappointed in EPA's decision to delay finalizing carbon pollution standards for existing gas plants, which make up a significant portion of carbon emissions in the power sector,'' said Frank Sturges, a lawyer for the Clean Air Task Force, an environmental group.

"Greenhouse gas emissions from power plants have gone uncontrolled for far too long, and we have no more time to waste," he said.

Other environmental groups hailed the decision, saying the new plan would ultimately deliver better results.

"We have always known that the fight for a clean power sector wouldn't be a quick one.,'' said Charles Harper of Evergreen Action. "EPA's first order of business should be finalizing strong and necessary limits on climate pollution from new gas and existing coal plants as quickly as possible.''

"We are glad that EPA is committed to finishing the job with a new rule that covers every gas plant operating in the U.S.,'' Harper added.

"Tackling dirty coal plants is one of the single most important moves the president and EPA can make to rein in climate pollution,'' said Abigail Dillen, president of Earthjustice. "As utilities propose new fossil gas plants, we absolutely have to get ahead of a big new pollution problem."

EPA issued a proposed rule in May 2023 that called for drastically curbing greenhouse gas emissions from existing coal and gas-fired plants, as well as future gas plants planned by the power industry. No new coal plant has opened in the U.S. in more than a decade, while dozens of coal-fired plants have closed in recent years in the face of competition from cheaper natural gas. The Biden administration has committed to create a carbon pollution-free power sector by 2035.

The EPA proposal could force power plants to capture smokestack emissions using a technology that has long been promised but is not used widely in the United States.

If finalized, the proposed regulation would mark the first time the federal government has restricted carbon dioxide emissions from existing power plants, which generate about 25% of U.S. greenhouse gas pollution, second only to the transportation sector. The rule also would apply to future electric plants and would avoid up to 617 million metric tons of carbon dioxide through 2042, equivalent to annual emissions of 137 million passenger vehicles, the EPA said.

Almost all coal plants -- along with large, frequently used gas-fired plants -- would have to cut or capture nearly all their carbon dioxide emissions by 2038, the EPA said. Plants that cannot meet the new standards would be forced to shutter.

Much of the EPA plan is expected to be made final this spring and is likely to be challenged by industry groups and Republican-leaning states. They have accused the Democratic administration of overreach on environmental regulations and warn of a pending reliability crisis for the electric grid. The power plant rule is one of at least a half-dozen EPA rules limiting power plant emissions and wastewater treatment.

The National Mining Association warned of "an onslaught" of government regulation "designed to shut down the coal fleet prematurely? when the EPA proposal was announced last year.

Regan has denied that the power plant rule is aimed at shutting down the coal sector, but acknowledged last year that, " we will see some coal retirements."

Coal provides about 20% of U.S. electricity, down from about 45% in 2010. Natural gas provides about 40% of U.S. electricity. The remainder comes from nuclear energy and renewables such as wind, solar and hydropower.

Peggy Shepard, co-founder and executive director of WE ACT for Environmental Justice, a New York-based group, said she was pleased that the concerns of environmental justice communities will be factored into EPA's rulemaking.

"The power sector is one of the top sources of carbon emissions and pollution,'' she said. "With this pause to take a deeper dive into developing the most comprehensive and thoughtful rulemaking for existing gas plants, we have an opportunity to do this work correctly and effectively to protect the human and environmental health of the most overburdened, neglected and vulnerable people across the country.''

The EPA's revised plan was first reported by Bloomberg News.