The Koch brothers’ conglomerate Koch Industries has refused to comply with an investigation by three Senate Democrats into whether the company has funded groups or researchers who deny or cast doubt on climate change.

In response to a request from senators Barbara Boxer, Edward Markey and Sheldon Whitehouse for information about Koch Industries’ support for scientific research, Koch general counsel Mark Holden invoked the company’s first amendment rights.

“The activity efforts about which you inquire, and Koch’s involvement, if any, in them, are at the core of the fundamental liberties protected by the first amendment to the United States constitution,” Holden wrote the senators in a letter dated March 5 and posted online by Koch Industries this week.

“I did not see any explanation or justification for an official Senate committee inquiry into activities protected by the first amendment,” he wrote, concluding, “we decline to participate in this endeavor and object to your apparent efforts to infringe upon and potentially stifle fundamental first amendment activities.”

Asked by the Guardian to elaborate on how the first amendment protects such funding and whether Koch Industries would pursue legal action to prevent disclosing information, Holden said: “Our letter speaks for itself.”

In his letter to the senators, Holden suggested that such funding represents part of “Koch’s right to participate in the debate of important public policy issues and its right of free association.”

On February 25, the three Democratic senators – each a ranking member of committees that oversee environmental affairs – sent letters to 100 fossil fuel companies and think tanks “to determine whether they are funding scientific studies designed to confuse the public and avoid taking action to cut carbon pollution, and whether the funded scientists fail to disclose the sources of their funding in scientific publications or in testimony to legislators.”

“Corporate special interests shouldn’t be able to secretly peddle the best junk science money can buy,” Markey said at the time. The senators asked for 10 years’ worth of information, including lists of affiliated foundations, funding recipients and copies of grants and contracts.

Exxon Mobil, BP and Shell are among the other companies sent letters by the senators. The libertarian Koch-founded Cato Institute and conservative Heritage Foundation were also sent letters.

The senators’ investigation was prompted by documents obtained through a freedom of information request by Greenpeace, the environmental group. The documents revealed a prominent Harvard-Smithsonian Center scientist had accepted more than $1.2m from the fossil-fuel industry. The scientist, Wei-Hock Soon, has espoused on television and before Congress alternate theories of climate change, including a discredited theory that the sun’s energy explain global warming.

Soon received at least $230,000 from the Charles G Koch Charitable Foundation, according to the documents obtained by Greenpeace. The Koch brothers, whose wide-ranging corporation extends into oil refineries, fertilizer production and polymers, paper and minerals, avidly inject cash into both political causes and cultural ones and do not always shy from the spotlight.

In January officials in the brothers’ political organization announced a budget of almost $1 billion would be available for the 2016 presidential field. David Koch has also leant his name to both the plaza at the Metropolitan Museum of Art in New York and an exhibit about human evolution at the Natural History Museum in Washington DC. The company recently began an advertising effort to rehabilitate its reputation and recast itself as an all-American operation.

Although Markey’s office did not immediately respond to a request for comment, a spokesperson said in a statement that “companies that are supporting legitimate, scientific inquiry should have no concerns about responding” to the senator’s request.

Holden is also senior vice-president of Koch Industries, and a board member of Freedom Partners, a nonprofit organization founded in 2011 as “the Association for American Innovation.” According to its 2012 tax returns, the organization has funneled more than $237m to other Koch-affiliated non-profits and to fund various research projects. Per the group’s website, it was “renamed to better reflect the organization’s mission.”

Originally published by The Guardian