In another jab to President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE's Environmental Protection Agency (EPA) head, actor and former California Gov. Arnold Schwarzenegger (R) labeled Scott Pruitt Edward (Scott) Scott PruittJuan Williams: Swamp creature at the White House Science protections must be enforceable Conspicuous by their absence from the Republican Convention MORE the worst EPA administrator of all time.

"I pay no attention to what he says. He cannot be taken seriously," Schwarzenegger said at the R20 Austrian World Summit, an annual climate conference he hosts in his home country. "He's the worst Environmental secretary that we have ever had."

Schwarzenegger went on to criticize Pruitt for his ties to oil and gas companies.

“He's doing the bidding for the oil companies and the coal companies," the 70-year-old Republican told Vice News at the summit.

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Schwarzenegger, an environmental activist, is leading an effort to sue oil companies for "knowingly killing people" through the burning of fossil fuels.

The former governor has taken jabs at Pruitt before, calling him the "wrong person" for the job months earlier, and taking to social media to criticize his policies.

In his address, Schwarzenegger urged Trump to join him and other activists in fighting climate change, despite efforts by the Trump administration to bolster the fossil fuel industry and its withdrawal from the Paris climate accord.

Pruitt has rolled back a number of the Obama administration's environmental policies, facing scrutiny from environmental advocates.

In the latest challenge to Pruitt's rollbacks, California is leading a coalition of states in suing the agency over its removal of fuel efficiency standards goals for automakers.

Pruitt also faces a number of investigations from ethics officials over reported extensive travels on taxpayer dollars, which have led numerous lawmakers to call for his resignation.