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.

The Wall Street Journal criticized Trump, accusing him of prioritizing “unions over workers,” while Fox News contributor Katie Pavlich called on Senate Republicans to “vote this nomination down.” She said: “A co-sponsor of the Pro-Act as Labor Secretary? Absolutely not.”

Democrats and the Teamster’s union welcomed the choice of Chavez-Deremer, however.

“Lori Chavez-DeRemer has been a champion for the American worker and will be the same as Labor Secretary,” said the Teamsters in a statement. “During her time in Congress, Chavez-DeRemer defended UPS workers’ right to strike and fought to protect the right to organize, raise working standards, and keep jobs from being shipped overseas.”