Sen. John McCainJohn Sidney McCainDon’t disrespect McCain by torpedoing his clean National Defense Authorization Act Meghan McCain rips Trump's 'gross' line about her dad Trump's America fights back MORE (R-Ariz.) said President Obama’s nominee to be a U.S. representative to the United Nations Human Rights Council was just the “latest bundler blunder nominee.”

Citing ethical concerns, some Senate Republicans have opposed Keith Harper’s nomination, because he was a former fundraiser for President Obama.

“Mr. Harper is just another example of a campaign bundler wholly unqualified for the position in which he is nominated,” McCain said ahead of the vote. “What [also] concerns me is his character.”

Harper, a member of the Cherokee Nation in Oklahoma, was a top bundler for the Obama’s presidential campaign in 2008 and a member of the administration’s transition team. He would be the first member of a federally recognized tribe to serve in an ambassador role.

McCain said Harper did a disservice to Native Americans when he served as co-counsel in the class-action lawsuit Cobell v. Salazar. The lawsuit resulted in a $3.4 billion settlement and Harper made millions from the deal. 

McCain said four Native Americans involved in the lawsuit didn’t want to accept the deal, but Harper and his legal team “bullied” them into it.

“He clearly abused these people’s human rights and now he’s going to be an ambassador on human rights?” McCain said.

The Senate Foreign Relations Committee cleared Harper’s nomination on a party-line vote in February. 

The Senate will vote to end debate on Harper's nomination around 5:30 p.m. on Monday. Last year, Senate Democrats used the “nuclear option” to unilaterally change the filibuster rules so that a simple majority can advance most nominations instead of the previously needed 60 votes.

Harper’s final confirmation is expected Tuesday.

— Jasmine Sachar contributed to this article.