More than 100 environmental groups began an eleventh-hour push Wednesday to block President Trump's pick for Interior Department deputy secretary, an agency veteran from the George W. Bush administration.

The groups sent a letter to all senators asking that they not support the nomination of David Bernhardt ahead of Thursday's confirmation hearing in the Senate Energy and Natural Resources Committee.

"Bernhardt has been called a 'walking conflict of interest' for good reason. He represents everything that's wrong with the Trump administration and the revolving door of politics," said Randi Spivak with the Center for Biological Diversity, a national conservation group that signed onto the letter. The group was the first to sue Trump over his planned border wall.

"It's clear he'll put the interests of oil, mining and agribusiness above the interests of the American people, public lands and wildlife," Spivak said.

The groups are playing up Bernhardt's representation of oil, coal and mining companies during his career in private legal practice as a major conflict of interest that will jeopardize the nation's federal lands.

"Mr. Bernhardt was one of the Bush administration's point people in the push to promote oil drilling from the Arctic to Wyoming," the letter said. "As [Interior's] solicitor he authored several controversial legal opinions, including one that stated the department could not use the Endangered Species Act to address the threats of climate change to polar bears even if the species was protected under the act."

The top Democrat on the energy committee, Sen. Maria Cantwell of Washington, is expected to lead the charge against Bernhardt's confirmation at the hearing.

Cantwell had opposed the appointment of Interior Secretary Ryan Zinke. She wasn't confident in Zinke's ability to defend public lands against expanded development and energy extraction activities.

Zinke is conducting a review to decide whether to rescind or reverse former President Barack Obama's significant expansion of national monuments under a recently signed executive order by Trump. The review is supposed to examine how the monument designations and expansions may have interfered with development opportunities.

Bernhardt would be Zinke's lieutenant as he seeks to also open up the nation's Atlantic coastline and the Arctic to new drilling opportunities under Trump's executive actions.

"Mr. Bernhardt has indicated that he plans to recuse himself from matters involving former clients for one year, and that he may not recuse himself if he receives authorization to work on such matters," the letter stated. "This is insufficient and unacceptable."

The groups want senators to press him on his recusal promises, adding that "he should not seek, accept or be granted any exemptions from issues that he may have a conflict," the letter read. "The Senate, at a minimum, must make this clear."

Democrats used the issue of recusal in an attempt to block Scott Pruitt's nomination to lead the Environmental Protection Agency. And they continue to prod the EPA administrator over his past role as attorney general of Oklahoma.

The groups added that the Department of the Interior "is charged with protecting our public lands, waterways and wildlife for future generations," but Bernhardt's "conflicts of interest, industry ties and questionable judgment make him ill-suited to lead the department, and his confirmation would place our most cherished natural resources at risk."