Environmental Protection Agency officials are in a standoff with the agency’s independent watchdog over a probe of EPA chief of staff Ryan Jackson’s efforts to influence a scientist ahead of her congressional testimony, with each side questioning the other’s legal authority.

In a letter released publicly Wednesday, acting EPA inspector general Charles J. Sheehan informed Congress that his office had encountered a “flagrant problem” in light of Jackson’s refusal to cooperate with an ongoing audit and investigation focused on his activities while in office.

“To countenance open defiance even in one instance — much less two, both by a senior official setting precedent for himself and all agency staff — is ruinous,” Sheehan wrote.

Agency officials have pushed back at the accusations, arguing that they had sought to accommodate the IG’s requests. “I have neither delayed nor refused to fully cooperate with EPA’s Inspector General,” Jackson wrote in a Nov. 5 letter to EPA Administrator Andrew Wheeler that was released by the agency.

On Thursday, Sheehan issued a blistering three-page critique of a legal opinion issued in connection with the quarrel, in which he said EPA General Counsel Matthew Leopold "grafts wide and wholesale evasions” on existing laws and policies.

The dispute, which involves two different probes, has escalated to a level not seen in at least six years. One former senior EPA official said that while the office has threatened to notify Congress about disputes multiple times in the past, “generally, cooler heads prevailed before that point.”

The EPA’s Office of Inspector General has launched several probes of top Trump appointees at the agency over the past 2½ years, most of which focused on former EPA administrator Scott Pruitt’s spending and management decisions. But it closed two of its biggest inquiries without reaching any conclusions a year ago, noting that it had failed to interview Pruitt before he resigned in July 2018.

Wheeler warned lawmakers in a Nov. 5 letter that one of the IG’s requests, that Jackson identify who provided him with an advance copy of the written testimony of environmental chemist Deborah Swackhamer, “implicates constitutional concerns.”

Swackhamer, who chaired the EPA’s Board of Scientific Counselors until Pruitt removed her and several other advisers in late 2017, criticized the Trump administration’s approach to science in testimony before Congress in May 2017. Shortly before she appeared, Jackson chastised her for not alerting the EPA’s congressional affairs staff that she planned to speak to lawmakers and questioned the accuracy of some of her remarks.

On June 26, 2017, top Democrats on the House Committee Science, Space and Technology demanded that the IG investigate the issue.

Jackson refused to tell IG investigators how he obtained Swackhamer’s testimony in advance, telling them, “I am not going to involve others or point fingers. … Welcome to Washington."

In a Nov. 5 opinion delivered to Wheeler, EPA General Counsel Matthew Z. Leopold questioned why the office would investigate a matter connected to a congressional hearing. “How Congress takes testimony or from whom it receives final testimony is not a proper area of inquiry for the OIG,” he said.

IG staffers have also questioned Jackson on the 2018 firing of Pruitt scheduler Madeline Morris, according to two federal officials, including what compensation she received from the agency after she stopped showing up at headquarters.

In his Nov. 5 letter, Jackson questioned the investigators’ tactics, noting that two investigators from the inspector general’s staff initially came to his office unannounced on July 23 to question him about a personnel matter. When they returned the following day, he said, they changed the topic of the discussion.

“I realized that the OIG investigators were trying to take advantage of a situation where I had not had the opportunity to review information or refresh my recollection on situations and matters from more than two years ago,” he wrote.

Thursday’s memo from the acting inspector general challenged both EPA officials’ assertion that they had tried to reach a compromise with his office, as well as their interpretation of the law.

Leopold’s view of the law, the memo states, “offers free rein to agency staff to refuse OIG requests for information... It would render us fundamentally dependent on an agency that ‘maintains control’ of information sought by the IG.”

In an email Thursday, EPA spokeswoman Corry Schiermeyer said it was “troubling" that the inspector general’s office continued to try to get Congress to intervene in the matter, saying it “undermines the cooperative" relationship the two offices enjoy.

“EPA has attempted to provide assistance to the Office of Inspector General, and we will continue to do so,” she said.