Environmental Protection Agency Administrator Scott Pruitt said Tuesday he plans to issue a directive next week to limit research grants provided by the agency to scientists serving on the agency's boards.

"If we have individuals who are on those boards receiving money from the agency, sometimes, to the tune of tens of millions of dollars, that calls into question the independence of the recommendations that come our way," Pruitt said at a Heritage Foundation event. "Next week, I will issue a directive that addresses that, to ensure the independence and transparency and objectivity with respect to the scientific advice that we are getting at the agency."

Pruitt didn't make clear if he would block scientists who receive grants from serving on the agency's scientific advisory committees or if he would simply impose restrictions on how grants are distributed.

An EPA spokeswoman would not provide further details.

The move likely will be criticized by environmentalists and Democrats who say the EPA under Pruitt does not respect science.

Pruitt already has overhauled the EPA's advisory boards. He dismissed half of the 18-member Board of Scientific Counselors earlier this year.

Some of the more than 130 candidates Pruitt is considering for the agency's Science Advisory Board question the legitimacy of climate change and promote the use of fossil fuels.

Pruitt also has removed an EPA web page focused on climate change and is encouraging the concept of a "Red Team/Blue Team" exercise, in which two groups of experts debate the science behind climate change. Many climate scientists blame greenhouse gases caused by burning fossil fuels for driving man-made climate change.

Republicans have long complained that the Obama administration favored filling EPA's advisory boards with scientists who backed its views on climate change.

House Republicans have unsuccessfully pursued legislation in recent years that would prevent recipients of agency grants from serving on EPA's boards.

Pruitt defended his approach to science and climate change before a friendly, conservative audience at the Heritage Foundation.

"With respect to climate change, it's not a question of whether climate change occurs: it does," Pruitt said. "It's not a matter of whether man contributes to it: we do. It's a question of how much do we contribute to it and how do we measure it with precision. The American people deserve an honest, transparent discussion about what we know and don't know with respect to [carbon dioxide]. It's never taken place."

The EPA administrator also indicated he would propose a modest replacement to the Clean Power Plan, the Obama administration regulation on carbon emissions that Pruitt announced last week he will repeal.

Pruitt argues the Obama administration based the Clean Power Plan on an expansive and illegal interpretation of the Clean Air Act by encouraging states to move away from coal to natural gas and transitioning to wind and solar power.

Pruitt told the Washington Examiner in an interview last month that he would seek to regulate power plants individually in a process known as "inside the fence line."

The EPA is bound to regulate emissions of carbon and other greenhouse gases under a 2009 agency rule known as the endangerment finding, so experts say Pruitt cannot simply repeal the Clean Power Plan without replacing it.

"I have to ask the question, what authority does the Clean Air Act give me on this issue to regulate CO2?" Pruitt said. "The Clean Air Act was set up to address local and regional pollutants, not the global phenomena of [greenhouse gases] and CO2. We have to ask what we know, and what can we do about it. I can't make that up. That's what the last administration did. Where is it in the Clean Air Act that EPA has the authority to declare war on any sector of our economy? I don't see it. That's what the last administration did, and it's ended under President Trump."