By a 21-6 vote, workers at an Amazon fulfillment center in Middletown, Del., rejected an effort to unionize Wednesday. It was the first such vote at a center, part of the Internet sales company’s U.S. distribution system.

While the number of unionized employees would have been small, Amazon worked hard to dissuade the technicians from organizing as part of the International Association of Machinists and Aerospace Workers. The Seattle-based company has fought unionization efforts in the past, closing a Seattle customer call center in 2000 when members began pushing for one.