A search warrant alleges the former CEO of a defense contractor funneled more than $150,000 through a shell company to the GOP senator's campaign.
The Maine senator is the first Republican to support Biden's historic pick to lead the federal agency with oversight of public lands and tribal obligations.
“I would be surprised if there was support in the Republican caucus if the bill comes out at $1.9 trillion," said Sen. Susan Collins of Maine.
The Senate has been much easier on his white nominees.
Joe Biden's nominee to run the White House Office of Management and Budget has elicited criticism for her partisan rhetoric online.
Collins joined six Republicans and every Senate Democrat to vote to convict former President Donald Trump last week.
White House press secretary Jen Psaki said the president would meet with the group on Monday “for a full exchange of views.”
However, the Maine Republican said, President Trump should be "afforded the opportunity" to challenge the election results.
A Trump-fueled turnout surge capped a GOP comeback over the final month of the campaign.
The Republican senator has won re-election against Democrat Sara Gideon.