President Biden offered his support on Sunday to union organizing efforts as Amazon workers at an Alabama warehouse vote on whether to unionize.

In a video posted on Twitter, the president told workers “in Alabama and all across America” that are considering joining a union that they face a “vitally important choice.”

He did not mention Amazon directly, but his video statement was released after almost 6,000 warehouse workers in Bessemer, Ala., started voting earlier this month on the option to join the Retail, Wholesale and Department Store Union (RWDSU). If approved, the union would become the first at Amazon’s U.S. operations.