Conservative activists and oil magnates Charles and David Koch slammed the Obama campaign for what they called “disturbing behavior” that is “at odds” with “the constitutional right to free speech.”

The allegations were made in an open letter written by Phillip Ellender, president of public affairs for the Koch Companies, in response to a fundraising letter from Obama campaign manager Jim Messina, in which Messina accused the Kochs of bankrolling “Tea Party extremism” and profiting from “jacking up prices at the pump.”

A number of media outlets have reported that the Koch brothers were looking to spend upwards of $200 million on various conservative activist groups, including the group they founded Americans for Prosperity (AFP), in an attempt to unseat President Obama.

Koch Industries has repeatedly denied that the explicit stated purpose of AFP is to defeat the president and contends that the organization is not “simply funded” by the Kochs, but rather by “tens of thousands of members and contributors from across the country.”

Mitt Romney and Rick Santorum campaigned at an event of the Michigan branch of the AFP on Saturday.

While the AFP is focused on fiscally conservative initiatives, the Kochs are significant donors to an array of organizations that, whether it is their stated purpose or not, are staunchly opposed to the president’s policies.

The letter took a less nuanced position against the Obama campaign claim that the Koch brothers were responsible for rising prices at the gas pump, an issue the president’s rivals have tried to pin on him in recent weeks.

“It is false that our business model is to make millions by jacking up prices at the pump,” the letter reads in part. “We own no gasoline stations and the part of our business you allude to, oil and gas refining, actually lowers the price of gasoline by increasing supply. Either you simply misunderstand the way commodities markets work or you are misleading your supporters and the rest of the American people.”

Ellender closed the letter by saying that the campaign’s attack on the Kochs, as private citizens who disagree with the president’s policies, is anathema to “the way a free society should operate.”

“That is why it is troubling to see a national political campaign apparently target individual citizens and private companies for some perceived political advantage,” the letter said. “I also hope the President will reflect on how the approach the campaign is using is at odds with our national values and the constitutional right to free speech.”

That mirrors the argument in favor of super-PACs, which is that campaign donations are a matter of free speech and should not be limited. 

The president told his donors in early February that they should support the super-PAC Priorities USA, which backs him. Republican-backing super-PACs outraised Priorities USA by millions of dollars in January.