Environmental Protection Agency Administrator Michael Regan said Friday that for states to block contaminated waste from a toxic train derailment in Ohio was "impermissible." 

"This is impermissible and this is unacceptable," he said, noting that there was no reason for states to block shipments of the type of waste that certified facilities routinely handle every day.

Some of the states have sought to block those shipments from being sent to hazardous waste storage sites. 

Oklahoma Gov. Kevin Stitt said last week that he had stopped waste from the derailment from coming into his state.

TRAIN CARRYING HAZARDOUS MATERIALS DERAILS IN NORTHWESTERN ARIZONA

Oklahoma Gov. Kevin Stitt

Kevin Stitt, governor of Oklahoma, listens during the Conservative Political Action Conference in Dallas, Texas, July 10, 2021. (Dylan Hollingsworth/Bloomberg via Getty Images)

The governor's office did not immediately respond to Fox News Digital's request for comment. 

In a letter to the states, the agency said that blocking the shipments was likely in violation of federal law, as well as the Commerce Clause of the U.S. Constitution, which the EPA said limits the power of states to stop the movement of hazardous waste.

The EPA told Norfolk Southern on Friday that it expects the rail operator to pursue legal action if it is unable to ship the waste to certified disposal facilities.

"A state that blocks these waste shipments may be impeding Norfolk Southern’s ability to comply with obligations under CERCLA, as well as EPA’s order to Norfolk Southern, which is unlawful," Regan told reporters, per The Hill. "We’ve been abundantly clear with our state partners that waste from East Palestine has been subject to more testing and more analysis … than other similar waste regularly accepted at facilities nationwide."

EPA Administrator Michael Regan speaking

FILE - Then-nominee for EPA Administrator, Michael Regan speaks at the Queen theater on Dec. 19, 2020, in Wilmington, Delaware.  (Joshua Roberts/Getty Images)

CERCLA, or the Comprehensive Environmental Response, Compensation, and Liability Act, provides a Federal "Superfund" to clean up uncontrolled or abandoned hazardous-waste sites as well as accidents, spills and other emergency releases of pollutants and contaminants into the environment.

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Regan also noted on Twitter Friday that cleanup following the derailment should be completed in about three months. Thus far, per the EPA, crews have removed nearly 5,500 tons of contaminated soil and 7 million gallons of wastewater.

"But let me be clear: @EPA ordered Norfolk Southern to clean up the mess it made — and no one should impede or prevent this cleanup as we return East Palestine to the beautiful community residents know it to be," he wrote. "That’s why I directed my team to issue two notifications: one to Norfolk Southern CEO Alan Shaw and the other to EPA’s co-regulators across the country. These letters remind both the company and our state partners of their legal obligations on waste management."

Ohio EPA and EPA contractors collect soil and air samples from the East Palestine derailment site

Ohio EPA and EPA contractors collect soil and air samples from the derailment site on March 9, 2023, in East Palestine, Ohio.  (Michael Swensen/Getty Images)

"The residents of East Palestine should expect that states, private companies and the federal government will work together to effectuate the swift cleanup they deserve. That’s exactly what EPA has set out to do, and we will not tolerate anything less," Regan asserted.

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Previously, the EPA had briefly stopped the contaminated waste removal when concerns were raised about oversight of where it was being shipped to sites in Michigan and Texas. Hazardous waste sites in Ohio and Indiana also have received shipments.

The Associated Press contributed to this report.