The Congresswoman from New York and Rep. Chellie Pingree (D-Maine) co-wrote an open letter Monday to the CEOs of Facebook, Google, and Microsoft that accuses them of giving their “implicit support” to climate change deniers.

“We were deeply disappointed to see that your companies were high-level sponsors of a conference this month in Washington D.C., known as LibertyCon, that included a session denying established science on climate change,” the congresswomen wrote.

The libertarian student-run conference hosted a variety of session and groups including one called the CO2 Coalition which, Mother Jones reports, handed out brochures to “explain how our lives and our planet Earth will be improved by additional atmospheric carbon dioxide.”

It should be noted that, according to the LibertyCon schedule, there was also a session titled “Are Carbon Taxes a Viable Solution for Climate Change?” in which two groups debated whether it could “help us take better care of the environment” or was “another ineffective tax grab?”

Although Facebook declined to comment on the letter or the conference, a spokesperson did direct Fortune to its sustainability page, explaining its commitment to fight climate change by reducing its “greenhouse gas footprint by 75% and reaching 100% renewable energy by 2020,” and noted that Facebook was a participant in the recent COP24 climate summit.

A Google spokesperson also emphasized the company’s dedication to environmental causes in an email to Fortune.

“Google has long been a leader in sustainability. Since 2007, we have operated as a carbon neutral company and in 2017, we reached 100% renewable energy for our global operations,” the spokesperson wrote. “Today, we have contracts to purchase nearly 3.5 gigawatts of output from renewable energy projects, making us one of the largest corporate purchasers of renewable energy in the world. To date, our renewable energy contracts have led to over $5 billion in new capital investment around the globe.”

As for its sponsorship of the conference, Google stressed to Mother Jones, which wrote about the event prior to the congresswomen’s rebuke, “We sponsor organizations from across the political spectrum to promote strong technology laws” and that sponsorship or collaboration doesn’t equate endorsement of agenda or ideas, as is stated in its public policy transparency report.

Microsoft did not respond to Fortune’s request for comment.

But the letter by Ocasio-Cortez and Pingree notes that past positive actions do not erase problematic behavior. And that monetary support isn’t as far from ideological support as the companies would like to believe.

In spite of being “encouraged” by the companies past initiatives to decrease their carbon footprint and find new energy sources, the Congresswomen warned, “The example you have set promoting sustainability and evidence-based science is compromised by your implicit support of the session.”

Particularly considering the dangers of misinformation campaigns, as Ocasio-Cortez tweeted.

We cannot allow the financing of misinformation campaigns to shape our democracy.

We can disagree on policy, but climate change is real. Period.

Proud to have joined @chelliepingree on this letter asking for greater responsibility to our democracy and planet. https://t.co/5hLsg1FmgT

— Alexandria Ocasio-Cortez (@AOC) January 28, 2019

“We cannot allow the financing of misinformation campaigns to shape our democracy,” Ocasio-Cortez said in a tweet. “We can disagree on policy, but climate change is real. Period.”

Chellie Pingree also noted in a tweet that even if companies “have made public commitments to reduce emissions,” she believed that “their sponsorship of a conference where climate change denial was promoted is dangerous and troubling.”

Corporations can’t be complicit in denying climate change. @Facebook, @Microsoft, & @Google have made public commitments to reduce emissions, but their sponsorship of a conference where climate change denial was promoted is dangerous and troubling to me & @AOC. Read our letter ⬇️ pic.twitter.com/0bLBcxW7Hf

— Congresswoman Chellie Pingree 🇺🇸 🇺🇦 (@chelliepingree) January 28, 2019

Ocasio-Cortez has made it clear that she thinks there needs to be a collective responsibility for reducing the impact of climate change—and that responsibility may fall particularly hard on wealthy companies and citizens.

While Monday’s letter calls for the world’s richest companies to use their power and pockets to set the tone social good, the Congresswoman has also implied that wealthy citizens who can afford to make the most impact on environmental change should be asked to do so.

Before taking office, Ocasio-Cortez suggested creating a “Select Committee for a Green New Deal,” which would focus on neutralizing U.S. economy greenhouse gas emissions. In order to pay for the program, she told Anderson Cooper on 60 Minutes earlier this month that she would be open a 70% income tax rate on the world’s richest people, as was done in the 1960s and 1970s.