(CNN) Joe Biden has not canceled a Thursday fundraiser co-hosted by a founder of a fossil fuel company despite criticism from climate activists who point to his pledge to turn away money from oil and gas industry executives.

Biden is scheduled to attend two high-dollar fundraisers Thursday in New York -- one of which is being co-hosted by Andrew Goldman, a former aide in Biden's Senate office who co-founded Western LNG, a Houston-based natural gas production and transportation company. Natural gas is a fossil fuel, according to the US Energy Information Administration, because it was "formed from the buried remains of plants and animals that lived millions of years ago."

His schedule did not change Thursday, even after Biden said Wednesday night he might reconsider attending the fundraiser with Goldman.

The controversy over the fundraiser illustrates progressives' skepticism of the approach to the 2020 race taken by Biden, the Democratic front-runner in national 2020 primary polls. His two chief challengers, Massachusetts Sen. Elizabeth Warren and Vermont Sen. Bernie Sanders, have decided not to hold fundraisers at all, instead relying mostly on online, small-dollar donors. Biden, though, regularly holds fundraisers, sometimes high-dollar affairs -- and faces increased scrutiny over his ties to individual donors because of those events.

All the top Democratic presidential contenders, including Biden, have signed the "No Fossil Fuel Money Pledge," a commitment to reject contributions of more than $200 from fossil fuel executives, lobbyists and political action committees.

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