Following a months-long standoff between the House Science Committee and state attorneys general conducting an investigation into Exxon over climate change denialism, Chairman Lamar Smith (R-TX) has called a hearing to affirm his right to subpoena the state officials overseeing criminal investigations.

Smith, a noted climate change denier, has made repeated demands that the attorneys general and several environmental groups turn over their communications about Exxon, accusing them of embarking on an “unprecedented effort against those who have questioned the causes, magnitude, or best ways to address climate change.” The attorneys general, as well as the activist groups, have refused to comply with the committee’s requests, setting up a battle over subpoena power.

In a June statement, the committee’s ranking member, Rep. Eddie Bernice Johnson (D-TX), said that Smith’s demands were “not about legitimate oversight,” but that the committee was “harassing” attorneys general investigating Exxon.

While Smith has previously conducted investigations into the executive branch and scientists funded by Congress, now the chairman has issued subpoenas to two state attorneys general conducting a criminal investigation. He made a wide-ranging request for communications the states had with each other, environmental groups, and the federal government about an “investigation or potential prosecution of companies, nonprofit organizations, scientists, or other individuals related to the issue of climate change.”

Several state attorneys general have been investigating whether Exxon Mobil lied to investors about climate change and how it could impact the company, specifically looking at whether the company’s statements to investors failed to include the company’s scientific research.

In their refusals to comply with Smith’s demands, the attorneys general of Massachusetts and New York have argued that the subpoenas are unprecedented, outside Congress’ purview, and an infringement on states’ rights. Massachusetts Attorney General Maura Healey’s chief legal counsel, Richard Johnston, called the subpoena “an unconstitutional and unwarranted interference with a legitimate ongoing state investigation.”

Johnson, the committee’s ranking member, also called the subpoena’s “unlawful.”

“As we and the various targets of these subpoenas have repeatedly pointed out, these actions are plainly unconstitutional. The Majority’s illegitimate actions set a very dangerous precedent and are one more step towards solidifying this Committee’s unfortunate new reputation as a committee of witch hunts,” Johnson said in a July statement.

But Smith has insisted that the committee is operating within its jurisdiction, arguing that the committee is looking into whether the state probes impose “an adverse impact on federally-funded scientific research” so that the committee knows whether to rejigger federal funding for research.

Now, Smith is holding a hearing on Wednesday to affirm his ability to subpoena state attorneys general. The committee will hear from legal experts in the hearing titled, “Affirming Congress’ Constitutional Oversight Responsibilities: Subpoena Authority and Recourse for Failure to Comply with Lawfully Issued Subpoenas.”

This is just Smith’s latest battle as chairman of the House Science Committee.

Since the beginning of his chairmanship, and particularly since the beginning of this Congress, Smith has embarked on several crusades regarding climate change. He has scrutinized the Obama administration’s proposed regulations of coal-fired power plants and pushed to cut NASA’s earth sciences budget.

And most prominently, Smith last year went after a climate study conducted by scientists at the National Oceanic and Atmospheric Administration (NOAA). He accused the scientists at NOAA of altering “data to get the results they needed to advance this administration’s extreme climate change agenda.” The committee’s investigation into NOAA culminated with subpoenas demanding scientists’ internal communications about the study, as NOAA repeatedly refused to hand over documents.

The Science Committee was one of several House committees that received new subpoena powers at the beginning of 2015. The chair can issue subpoenas without consulting the committee’s ranking member, and Smith has not shied away from using that power.

“The amount of power that he has and that he’s exercising is unprecedented for the Science Committee,” Mark Harkins, a senior fellow at Georgetown University’s Government Affairs Institute and former Democratic staffer on the Science Committee, told TPM.

Harkins said that House Science Committee has been historically bipartisan, and David Goldston, a former Republican staffer on the Science Committee who now serves as the director of government affairs at the National Resources Defense Council, agreed.

“There wasn’t the sort of kind of deep fundamental divide and distrust that there appears to be now,” Goldston said of his work on the committee in the early 2000s, adding that the Science Committee’s majority is now “far more dominated by people who are more ideological.”

But Goldston emphasized that any change in the way the Science Committee goes about its work isn’t entirely unique to the committee, but “part of the overall, evermore complete, ideological polarization of the House.”