Story highlights Scientists and environmentalists want chemical plant rule to stand, despite opposition from fossil fuel groups

EPA Administrator Scott Pruitt previously wrote letter to EPA denouncing rule

Washington (CNN) Fossil fuel lobbyists and environmentalists have kick-started a legal battle over whether the Trump administration will defend regulations on chemical plant safety.

The Union for Concerned Scientists, Sierra Club and Earthjustice jointly filed a motion Thusday 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.

Read More