NEW YORK (CBSNewYork/AP) — Tensions were mounting among the presidential candidates Friday, just four days away from another major primary contest.

As CBS2’s Alice Gainer reported, the Wisconsin primary is set for Tuesday of next week, and early voter turnout is up by more than 400 percent.

READ MORE: Liberty Science Center Breaks Ground On $300 Million SciTech Scity Expansion

The friction between Democrats Bernie Sanders and Hillary Clinton has been growing in New York. Sanders spoke out Friday after Clinton said she was “sick of the Sanders campaign lying” about donations she’s received from the fossil fuel industry.

In an interview Friday on “CBS This Morning,” Sanders cited a Greenpeace study that said Clinton received over $4 million from the fossil fuel industry with individual contributions from over 50 lobbyists, CBS News reported.

COMPLETE CAMPAIGN 2016 COVERAGE

“If people receive money from lobbyists of the industry, I think you’re receiving money from the industry,” Sanders said.

On Thursday, Clinton’s team accused Sanders’ campaign of “misleading voters with their attacks,” after she was confronted by a Greenpeace organizer who asked whether she’d forego contributions from the fossil fuel industry at a campaign event.

“I am so sick of the Sanders campaign lying about me,” she said. “I am so sick of it.”

According to Factcheck.org, Clinton’s campaign hadn’t received any direct contributions from any corporation, including the gas and oil companies, Charlie Rose told Sanders on “CBS This Morning” on Friday.

READ MORE: Watch CBS2’s Candidate Conversation With New Jersey Gubernatorial Candidate Jack Ciattarelli

“If you are a lobbyist for the fossil fuel industry and there are 50 of you and you make a contribution, that, to me Charlie, is a contribution from the fossil fuel industry,” Sanders responded. “That’s different than saying you get it from Exxon Mobil.”

Clinton spokesman Nick Merrill said she had never accepted funds from oil and gas industries, companies or their political action committees. Both candidates, he said, have taken contributions from individuals who work in the industry.

“Assuming they don’t believe their own candidate is bought by the fossil fuel industry, they should stop the false attacks,” Merrill said.

An estimated 15,000 people showed up Thursday night when Sanders spoke in St. Mary’s Park in the Bronx. Clinton appeared Friday in Syracuse.

A total of 247 delegates are at stake in New York state. Clinton has a 12-point lead.

But polls showed Sanders had an edge over Clinton in Tuesday’s Wisconsin primary, after winning the last three states.

Clinton also lashed out at Sanders, criticizing his plans for free college tuition and dismissing them as unrealistic.

Ohio Gov. and Republican presidential candidate John Kasich also took a shot at Sanders’ plans for free college Friday while campaigning in Pennsylvania.
“Do you believe we can have free college?” Kasich said. “OK, so just tell people — be realistic, folks.”

In the Republican race, Donald Trump’s chances to win before the Republican National Convention could be in jeopardy if he loses in Wisconsin on Tuesday. He trails Ted Cruz by 10 points in the latest polls.

MORE NEWS: Early Voting Begins Saturday In New York City, New Jersey

(TM and © Copyright 2016 CBS Radio Inc. and its relevant subsidiaries. CBS RADIO and EYE Logo TM and Copyright 2016 CBS Broadcasting Inc. Used under license. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.)