Originally Published: 13 JUL 23 16:48 ET

Updated: 13 JUL 23 17:45 ET

By Manu Raju and Arlette Saenz, CNN

(CNN) — 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.

Biden continued to back Su after Manchin’s statement.

“President Biden and his team continue fighting for Acting Secretary of Labor Julie Su’s confirmation – because she is highly-qualified, experienced, and has proven herself time and time again when it comes to delivering for America’s workers and our economy,” a White House official said. “The President’s support for Acting Secretary Su is unwavering, and we hope Senator Manchin and Senator Sinema reconsider their position.”

While Manchin did voice his opposition to Su today, Sen. Kyrsten Sinema of Arizona has yet to publicly lay out her position.

This story has been updated with additional developments.