Sen. Rand Paul, a Kentucky Republican known to be an ally of Donald Trump, has nevertheless announced he won’t support the president’s pick to lead the Labor Department.

The senator told Fox News Radio correspondent Ryan Schmelz and NBC News senior political reporter Sahil Kapur that he would vote “no” on Lori Chavez-DeRemer’s confirmation, citing her “very pro-labor” views as the key factor behind his decision.

“I think she’ll lose 15 Republicans and she’ll get 25 Democrats,” he told Schmelz. “I mean, she’s very pro-labor. She might get all the Democrats. Who knows.”

Trump nominated Chavez-DeRemer as his Secretary of Labor in November, specifically highlighting her commitment to supporting American workers.

“Lori’s strong support from both the Business and Labor communities will ensure that the Labor Department can unite Americans of all backgrounds behind our Agenda for unprecedented National Success,” he said at the time. “Making America Richer, Wealthier, Stronger and more Prosperous than ever before!”

Pro-business and anti-union groups swiftly voiced concerns over the nomination, including the Coalition for a Democratic Workplace, which stated it was “alarmed” by President Trump’s decision.