A visibly angry Hillary Clinton lashed out at an environmental activist Thursday while accusing the Bernie Sanders campaign of “lying” about donations sent from the fossil fuel industry to her campaign.

“I am so sick, I am so sick of the Sanders campaign lying about me. I’m sick of it,” Clinton told Eva Resnick-Day of Greenpeace, who confronted the Democratic presidential front-runner on the rope-line after a campaign stop in New York. Clinton acknowledged that some of her donors work for fossil fuel companies.

Greenpeace released video of the encounter, which showed Clinton jabbing her finger at the activist. The former New York senator also appeared frustrated earlier in the day when Sanders supporters interrupted her speech, shouting “she wins, we lose” in unison before being escorted out of the event at SUNY Purchase.

view photo essay Political Theatre: The presidential campaign of Hillary Clinton Clinton arguably boasts experience in government unparalleled by anyone in the presidential field — but that has also made her a high-profile target for attack.

Employees of oil and gas companies, however, have contributed $307,000 to Clinton’s campaign,

to the Center for Responsive politics, while Sanders has received $54,000.

FactCheck.Org in December found that Clinton had not taken any money from PACs tied to the oil and gas industry, or companies themselves.

Greenpeace claims Clinton has taken $4.5 million from lobbyists, bundlers, and large donors connected the fossil fuel industry. However, the vast majority of that – $3.25 million – went to a super PAC supporting Clinton, with which she is legally barred from coordinating.

Sanders’ campaign was also eager to call attention to the encounter. “The truth is that Secretary Clinton has relied heavily on funds from lobbyists working for the oil, gas and coal industry,” said Sanders spokesperson Michael Briggs, citing the Greenpeace research.

But Clinton’s campaign said the former secretary of state has been a leader on climate change. “The simple truth is that this campaign has not taken a dollar from oil and gas industry PACs or corporations. The simple fact is that the Sanders campaign is misleading voters with their attacks,” spokesperson Nick Merrill said in a statement. ”The money in question is from individuals who work for these companies. By the same metric, Bernie Sanders has taken more than $50,000 on this campaign from individuals working for oil and gas companies. Assuming they don’t believe their own candidate is bought by the fossil fuel industry, they should stop the false attacks and do what they’ve claimed the campaign is about: debating the issues.”

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Sanders has made an issue of Clinton’s contributions from employees of energy companies and the financial sector.

“Just as I believe you can’t take on Wall Street while taking their money, I don’t believe you can take on climate change effectively while taking money from those who would profit off the destruction of the planet,” Sanders told a Minnesota crowd in late February. The Sanders campaign also ran an ad that suggested he was the only candidate who could stand up to big oil, “because he won’t take their money.”

Clinton has been asked about fossil fuel contributions on several occasions in the past, but never responded so aggressively.

“I don’t even know what you’re referring to. But big oil knows I’m not their friend,” Clinton said at a town hall in Dover, New Hampshire when a voter raised the issue.

Challenged in Iowa to sign a pledge not take donations from the fossil fuel industry, Clinton replied, “I don’t know that I ever have, I’m not exactly one of their favorites.” When the voter informed Clinton she actually had, the candidate responded, “Have I? OK, well, I’ll check on that.” Clinton did not sign the pledge, but Sanders and former candidate Martin O’Malley did.

“I’ve been at Hillary Clinton events around the country at rallies where activists have been asking her to stop taking fossil fuels and I was shocked and surprised at her reaction to my question,” Resnick-Day said in statement. ”Secretary Clinton needs to listen to the people, not fossil fuel interests.”

Whenever she is asked about the issue, Clinton reiterates that she wants to move away from fossil fuels and towards renewable energy and is committed to addressing climate change.