WASHINGTON (CNN) -- Fossil fuel lobbyists and environmentalists are set for a legal battle over whether the Trump administration will defend regulations on chemical plant safety.

The Union for Concerned Scientists, Sierra Club and Earthjustice plan to jointly file a motion Wednesday to intervene in a lawsuit filed by fossil fuel groups in March that asks the Environmental Protection Agency to delay or reconsider a rule that places more regulations on chemical plants. The chemical plant regulations were signed into the Federal Register in January as a direct response to the fertilizer plant explosion in West Texas that killed 15 and injured more than 160 in 2013.

"We don't know for sure whether EPA will defend it or not, but given the fact that (EPA) Administrator (Scott) Pruitt has in the past opposed this regulation, I don't think it's out of the realm of possibility that we won't get EPA out there defending the rule," said Yogin Kothari, Washington representative with the Center for Science and Democracy at the Union of Concerned Scientists.

Pruitt has voiced objection to the EPA's Accidental Release Prevention Requirements in the past, writing a letter in 2016 while he was Oklahoma Attorney General to then EPA Administrator Gina McCarthy urging her to rethink course on the rule.

Pruitt and 10 other attorneys general, including Florida's Pam Bondi, asked the EPA to consider national security concerns in the regulations. Part of the ARPR would allow the public to inquire about the nature of the chemicals held at facilities nearby. Supporters of the requirement argued the knowledge would help public safety and readiness, but Pruitt and others argued the information could make the facilities targets for terrorism.

"The safety of these manufacturing, processing and storage facilities should be a priority for us all, but safety encompasses more than preventing accidental releases of chemicals, it also encompasses preventing intentional releases caused by bad actors seeking to harm our citizens," Pruitt said in the letter.

The EPA regulations on chemical plants came to fruition following an Obama-era executive order signed in 2013 to revisit those regulations following the West Texas accident. The regulations are also intended to improve coordination between facilities and first responders.

In March though, a group of fossil fuel groups including the American Chemistry Council, American Fuel and Petrochemical Manufactures and American Petroleum institute sued the EPA to petition a review of the final rule, arguing in the suit it is "unlawful, arbitrary, capricious, an abuse of discretion, and not otherwise in accordance with law."

Additionally, the group asked the EPA to consider a 90-day freeze on implementing the rule.

Early in the year, a group of Republican members of Congress also made it clear their dislike for the rule and introduced a joint House and Senate resolution showing congressional disapproval of the regulation and asking to nullify it.

Environmental groups see both efforts as stalling tactics for a rule that has taken two years to be signed.

"We see that this rule as an important rule to have on the books," Kothari said. "We see it as a modest improvement over the current regulations and we see it as a way to protect workers, first responders and low income communities and communities of color, which are often living right next to these chemical plants."

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