Bernie Sanders Demands Apology From Hillary Clinton for Accusing Him of Lying

The back and forth between Sanders and Clinton has reached a fever pitch.

Speaking to a packed house eastern Wisconsin, Sanders twice said Clinton owed his campaign an apology.

“We were not lying, we were telling the truth,” the presidential hopeful said after bringing up an incident yesterday in which an activist asked Clinton if she would stop taking money from the fossil fuel industry. Clinton responded aggressively and accused the Sanders' campaign of lying.

But the Clinton campaign has not given an inch either. Clinton's National Communication Director Jen Palmieri said today they will not apologize. "Despite their pledge to run a positive campaign about the issues, we have seen increasingly ratcheted-up personal attacks from Senator Sanders, his campaign and their surrogates," she said in a statement. "It’s disappointing that they’ve doubled down on negative character attacks that deliberately mislead voters rather than debate the issues.

"Their latest attack over campaign contributions ignores their own donations from individuals who work for oil and gas companies, and most importantly it ignores Hillary Clinton’s record and agenda. 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."

Yesterday, the Clinton campaign pointed to additional documents, which show that employees from oil and gas companies have given to both campaigns. According to the Center for Responsive Politics, employees of oil and gas companies have contributed $307,000 to Clinton’s campaign, but also have given $54,000 to Sanders’ campaign.

Sanders seemed to respond to this as he pointed out in his remarks that the contributors with ties to oil and gas cited in the Greenpeace report were “not just workers in the fossil fuel industry, these are paid registered lobbyists.”

ABC News' Liz Kreutz contributed to this report.