Julie Su, President Joe Biden's pick to be the next Labor secretary whose nomination has been stalled for months, now faces opposition from a key Democrat: Sen. Joe Manchin of West Virginia.

With all Republicans planning to oppose her, she can only afford to lose one more member of the Senate Democratic Caucus -- and several remain non-committal.

"I believe the person leading the U.S. Department of Labor should have the experience to collaboratively lead both labor and industry to forge compromises acceptable to both parties," Manchin said in a statement Thursday. "While her credentials and qualifications are impressive, I have genuine concerns that Julie Su's more progressive background prevents her from doing this and for that reason I cannot support her nomination to serve as Secretary of Labor."

Su, currently the Department of Labor's acting secretary, first joined the Biden administration in 2021 as the deputy secretary of labor. She was confirmed to the role with the unanimous support of Democrats in the Senate and no support from Republicans.

Biden nominated Su to permanently lead the Labor Department at the end of February.