U.S. Senate Republicans are threatening to hold up President Barack Obama’s nominations to fill three top positions at the Environmental Protection Agency (EPA), including the agency’s top science and research official. At a committee hearing yesterday, Republicans complained that EPA has continually stonewalled their requests for data and information and said that blocking nominees is their only recourse. But Democrats called for advancing the otherwise noncontroversial nominees, who have been awaiting confirmation for 2 years.

Some senators also raised questions about EPA’s plan to have the researcher nominated to head its science office also serve as the agency’s science adviser, saying it could create conflicts of interest.

If Republicans make good on the threat, it would pose a new roadblock to the nomination of Thomas Burke, an epidemiologist, to serve as the assistant administrator for the agency’s Office of Research and Development (ORD). The president nominated Burke—currently EPA’s science adviser and deputy assistant administrator for ORD—for the same post in the previous Congress, but the Senate never confirmed him. Also at stake are the nominations of Ann Dunkin to oversee EPA information programs, and Jane Nishida to handle international and tribal issues.

Speaking at the 11 June hearing of the Senate Environment and Public Works Committee, Senator Dan Sullivan (R–AK) lamented that EPA chief Gina McCarthy hadn’t responded to a number of Republican requests, including for copies of legal opinions underpinning EPA moves to strengthen water pollution and climate rules. He asked the three nominees whether it was reasonable to hold up the nominations until McCarthy responded; all declined to answer.

Senator Barbara Boxer (D–CA) noted that the committee had advanced these nominees to the Senate floor on voice votes nearly 2 years ago. It’s unreasonable for Republicans to hold up these nominations, she suggested, especially given their qualifications. “If we can’t get you people moving toward the floor, I don’t know who would be better,” said Boxer, the committee’s top Democrat.

The stalemate has left Burke, currently EPA’s science adviser, hanging. Prior to becoming science adviser in 2014, Burke, an epidemiologist by training, served as an associate dean of the Johns Hopkins Bloomberg School of Public Health in Baltimore, Maryland. He has also held high-level positions in New Jersey’s public health and environmental agencies. And he has served on many EPA science advisory panels and National Academy of Sciences (NAS) panels.

As head of ORD, Burke would be responsible for administering a number of grant programs and EPA’s in-house laboratories, as well as helping formulate how the agency should use science—from risk assessment to analytical tools to modeling to toxicology research—to guide its policies.

Since the departure of Paul Anastas, a Yale University green chemist who simultaneously served as both ORD chief and science adviser from 2009 to early 2012, ORD has lacked a permanent head; Lek Kadeli has served as the acting chief. Meanwhile, Glenn Paulson served as Anastas’s successor as science adviser until last year.

Burke’s nomination has been noncontroversial. But at yesterday’s hearing Senator James Inhofe (R–OK), the committee’s chairman, said he was concerned about having Burke serve as both ORD chief and EPA science adviser, as Anastas once did. Inhofe noted that an NAS report found that such an arrangement could create a conflict of interest—for example, if the science adviser was asked to advise the EPA administrator on priorities for ORD’s budget.

Burke told Inhofe that he didn’t see a problem, noting that he had taken part in NAS discussions on the matter before coming to EPA. “I know there have been different perspectives on science adviser being separate from the assistant administrator,” Burke said. “I think the most important message, though, is that there be clear and consistent leadership for science at the agency.”

Whether Senate Republicans will enable him to be confirmed to his new leadership position remains to be seen.