Environmental Protection Agency Administrator Scott Pruitt has chosen to replace half of the members on one of its key scientific review boards, the first step in a broader effort by Republicans to change the way the agency evaluates the scientific basis for its regulations.

The move could significantly change the makeup of the 18-member Board of Scientific Counselors, which advises EPA's key scientific arm on whether the research it does has sufficient rigor and integrity. All of the members being dismissed were at the end of serving at least one three-year term, although these terms are often renewed instead of terminated.

EPA spokesman J.P. Freire said in an email that "no one has been fired or terminated," and that Pruitt had simply decided to bring in fresh advisers. The agency informed the outside academics on Friday that their terms would not be renewed.

"We're not going to rubber-stamp the last administration's appointees. Instead, they should participate in the same open competitive process as the rest of the applicant pool," Freire said. "This approach is what was always intended for the Board, and we're making a clean break with the last administration's approach."

But the move came as a surprise to members of the board, who had been informed both in January, before Barack Obama left office, and then more recently by EPA career staff members, that they would be kept on for another term.

"I was kind of shocked to receive this news," Robert Richardson, an ecological economist and an associate professor at Michigan State University's Department of Community Sustainability, said in an interview Sunday.

Richardson, who tweeted on Saturday, "Today, I was Trumped," said that he was at the end of an initial three-year term on the board, but that board members traditionally have served two such stints. "I've never heard of any circumstance where someone didn't serve two consecutive terms," he added.

Courtney Flint, a professor of natural resource sociology at Utah State University who had served one term on the board, said in an email that she was also surprised to learn that her term would not be renewed, "particularly since I was told that such a renewal was expected."

"In the broader view, I suppose it is the prerogative of this administration to set the goals of federal agencies and to appoint members to advisory boards," she added.

The terms of at least 12 members of the board ended April 27, according to a federal database, making them eligible for replacement.

Ryan Jackson, Pruitt's chief of staff, noted in an email that all the board members whose terms are not being renewed could reapply for their positions.

"I'm not quite sure why some EPA career staff simply get angry by us opening up the process," he said. "It seems unprofessional to me."

Pruitt is planning a much broader overhaul of how the agency conducts its scientific analysis, said a senior administration official who spoke on the condition of anonymity to discuss internal deliberations. The administration has been meeting with academics to talk about the matter and putting thought into which areas of investigation warrant attention from the agency's scientific advisers.

The agency may consider industry scientific experts for some of the board positions, Freire said, as long as these appointments do not pose a conflict of interest.

Conservatives have complained about EPA's approach to science, including the input it receives from outside scientific bodies, for years. Both the Board of Scientific Counselors and a larger, 47-person Scientific Advisory Board have come under criticism for bolstering the cause for greater federal regulation.

Sen. James Inhofe, R-Okla., who questions the link between human activity and climate change and has several former aides now working for Pruitt, said in an interview earlier this year that under the new administration, "They're going to have to start dealing with science and not rigged science" at EPA.

House Science Committee Chairman Lamar Smith, R-Texas, held a hearing on the issue in February, arguing that the composition of the Scientific Advisory Board, which was established in 1978, should be expanded to include more non-academics. It is primarily made up of academic scientists and other experts who review EPA's research to ensure that the regulations the agency undertakes have a sound scientific basis.

"The EPA routinely stacks this board with friendly scientists who receive millions of dollars in grants from the federal government," Smith said at the time. "The conflict of interest here is clear."

In a budget proposal obtained by The Washington Post last month, the panel is slated for an 84 percent cut — or $542,000 — from its operating budget. That money typically covers travel and other expenses for outside experts who attend the board's public meetings.

The reasoning behind the budget cut, said the document, reflects "an anticipated lower number of peer reviews."

The Washington Post's Chris Mooney contributed to this report.