The Environmental Protection Agency in an unexpected move Wednesday night canceled its one-year delay of the Obama administration's strict rules for smog-forming ozone emissions, prompting Democratic state attorneys general to claim victory after suing the agency the night before.

"Just 1 day ago, I led a coalition of 16 AGs in suing @EPA for failing to protect kids from smog. Tonight, the Trump @EPA reversed course," tweeted New York Democratic Attorney General Eric Schneiderman. EPA must enforce the regulations beginning Oct. 1.

EPA Administrator Scott Pruitt signed an order Wednesday night that canceled the one-year delay that he had imposed last month to stall implementation of the 2015 ozone emission rules as the agency moves forward with a review to revise or rescind the regulations. Pruitt said Wednesday's reversal "reinforces our commitment to working with the states through the complex designation process."

The sudden cancellation of the EPA delay came days after the D.C. Circuit Court of Appeals ordered the agency to begin enforcing the Obama-era EPA rules on methane emissions for the oil and natural gas industry. Pruitt had sought to delay that rule for three years, but the court said the agency did not have the legal authority to carry out such a long delay of a final regulation. The court issued a second order clarifying that the agency must now enforce the methane rules.

Environmental groups suggested that Pruitt's sudden Wednesday night decision may have been in anticipation of the D.C. Circuit Court ruling the same on ozone as it did on the methane emission delay. "The EPA's hasty retreat shows that public health and environmental organizations and 16 states across the country were right: the agency had no legal basis for delaying implementation of the 2015 smog standard," said Seth Johnson, an attorney with the group Earthjustice that sued the EPA last month for imposing the delay.

The oil and gas industry is adamant that the ozone regulations are not needed, especially with evidence showing that pollution is decreasing under the previous 2008 standards, according to the American Petroleum Institute. The oil industry argues that the EPA should roll back the 2015 standards because states have not complied with the previous regulations.

"Implementing both the 2008 and 2015 standards creates unnecessary complexity and inefficiency, in addition to needlessly burdening the states and businesses with potentially enormous costs to implement dual standards and competing timelines," said API's regulatory director Howard Feldman in a Thursday morning statement. "Energy security, economic and environmental progress can be complementary goals.

"Increased use of cleaner-burning natural gas for power generation has led to U.S. carbon emissions from power generation reaching near 30-year lows and has contributed to the significant decreases in emissions of many common air pollutants, according to EPA's latest report. Progress can continue under existing rules while we continue to power a growing economy," Feldman said.

He said the industry will look to the EPA and Congress to enact "achievable timelines and smart legislation." The House passed legislation last month to rein in the 2015 ozone rules in line with industry concerns.