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SHEBOYGAN, Wisconsin — Senator Bernie Sanders said that his Democratic presidential primary opponent former Secretary of State Hillary Clinton owed him and his campaign an apology Friday evening over an ongoing spat about donations from the fossil fuel industry.

"Secretary Clinton, you owe us an apology. We were telling the truth,” Sanders in response to accusations from Clinton's campaign that he and his campaign had been “lying" and misconstruing Clinton’s relationship with the oil and gas industry.

“The truth is that Secretary Clinton has relied heavily on funds from lobbyists working for the oil, gas, and coal industry,” Sanders said in front of a crowd of about 2,200 people in Sheboygan South High School.

Sanders argued that Clinton’s campaign and Super PAC has received "more than $4.5 million from the fossil fuel industry" and said "57 oil, gas, and coal industry lobbyists have directly contributed to her campaign" citing an analysis done by the environmental organization Greenpeace.

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The Clinton team quickly responded, saying they would not apologize. Clinton's campaign said Sanders was going out of his way to "deliberately mislead voters rather than debate the issues."

"We will not apologize for calling out these kinds of schemes for what they are: a desperate move from a campaign that has clearly decided that the only hope for a path to victory is through misleading attacks," Clinton campaign communications director Jennifer Palmieri said in a statement to NBC News.

Palmieri also said the Sanders campaign has received campaign contributions from "individuals who work for oil and gas companies."

Between this most recent back-and-forth and Clinton’s critiques of Sanders’ response to GOP front-runner Donald Trump’s controversial remarks on abortion, this week has become one of the most contentious weeks in the Democratic primary race thus far.

The controversy started Thursday when a video came out on social media showing an activist from Greenpeace confronting Clinton on the issue of fossil fuel industry contributions at a rally at SUNY Purchase in Purchase, New York.

Clinton started to answer the question before getting visibly angry and shaking her finger at the young woman. "I have never ... I am so sick, I am so sick of the Sanders campaign lying about me. I am sick of it," she said forcefully.

Since then, an ongoing debate has erupted between the two campaigns over the fossil fuel industry’s influence in the democratic race.

The Sanders campaign is standing by the Greenpeace analysis, which examines almost $1.5 million bundled for the campaign by lobbyists for the fossil fuel industry and over $3.2 million from "large donors" with fossil fuel interests for the Clinton backing Super PAC, Priorities USA.

Clinton’s campaign has pushed back hard, pointing to the Center For Responsive Politics which shows Clinton receiving over $300,000 from the "Oil and Gas" industry, but also Sanders receiving over $54,000 from the sector. This list focuses primarily on employees who work in either oil or gas.