WASHINGTON (Reuters) - Two Democratic senators said on Wednesday they may hold up the confirmation of President Donald Trump’s Environmental Protection Agency nominee Susan Bodine until she explains her advisory role at the agency, which may violate federal law.

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Senators Sheldon Whitehouse of Rhode Island and Jeff Merkley of Oregon sent a list of questions to Bodine, Trump’s pick to head up the EPA’s Office of Enforcement and Compliance Assistance, about her current role as special counsel to EPA Administrator Scott Pruitt while she waits out the confirmation process.

Whitehouse and Merkley said by advising Pruitt on enforcement matters before being confirmed by the Senate, Bodine may be violating the Federal Vacancies Reform Act that prohibits nominees from assuming the authorities of the office before being confirmed by Congress.

“Your appointment creates the appearance, and perhaps the effect, of circumventing the Senate’s constitutional advice and consent responsibility for the position to which you have been nominated,” the Senators wrote.

This means that subjects of EPA enforcement actions could potentially challenge the validity of these actions in court if her role in these decisions is deemed “improper,” they said.

Pruitt is the only EPA appointee to have been confirmed since Trump took office in January. Bodine is still awaiting a full Senate vote after her Senate confirmation hearing in July, while four other assistant administrator nominees are set for confirmation hearings on Sept. 20.

Democratic lawmakers have been at odds with Pruitt since his narrow-margin confirmation in February over his close ties to industry, his doubts about human-caused climate change, planned drastic cuts of the EPA’s budget and workforce and ethics requirements for political appointees.

The senators also asked Bodine if she was involved in a recent EPA decision to enforce an Obama-era rule to regulate methane leaks from new oil and gas infrastructure on a “case by case” basis rather than fully enforcing it.

Republican Senator John Barrasso of Wyoming, chair of the Senate environment committee, said Bodine should get her full Senate vote immediately.

“It is a shame that the critical post of the assistant administrator charged with leading enforcement at the EPA remains unfilled,” Barrasso said through a spokesman.

The EPA was not immediately available for comment.