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By Nick Carey

CHATTANOOGA, Tenn., June 14 (Reuters) - Workers at Volkswagen AG's assembly plant in the state of Tennessee narrowly voted against union representation, dealing a fresh blow to the United Auto Workers' (UAW) efforts to unionize a foreign automaker's plant in the U.S. South.

The German automaker and the UAW said on Friday that workers at the Chattanooga plant voted 833 to 776 against union representation, the second time in five years they have rejected collective bargaining.

"Our employees have spoken," Frank Fischer, president of Volkswagen Chattanooga, said in a statement. "Pending certification of the results... Volkswagen will respect the decision of the majority."

Speaking to reporters in Chattanooga, UAW spokesman Brian Rothenberg claimed that Volkswagen had engaged in "threats" and "intimidation" that had affected the outcome of the vote.

"The company kept playing a lot of games and we are not going to abandon the workers who supported a union," he said.

Rothenberg said it was too early to tell whether the UAW would appeal the election results, or whether the union would support another vote at the plant.

The fresh defeat comes at a pivotal time for the UAW, which has been struggling to move beyond a federal corruption probe and faces contentious contract talks this year with General Motors Co, Ford Motor Co and Fiat Chrysler Automobiles NV .

The loss also raises renewed questions about whether the UAW can gain a toehold in the U.S. South and organize workers at a foreign automaker.

The union's membership peaked at 1.5 million in 1979 and despite gains this decade, it fell to below 400,000 last year.

The UAW narrowly failed to organize VW's Chattanooga plant in 2014. The vote this week was closer than the one five years ago, which was 712 against to 626 for unionization.

In 2017, workers at a Nissan Motor Co Ltd plant in Canton, Mississippi, voted nearly two to one against union representation.

Ahead of the vote, prominent Republican elected officials in Tennessee, including U.S. Senator Marsha Blackburn, had argued publicly against unionization at the Chattanooga plant.

Harley Shaiken, a labor expert at the University of California-Berkeley, said without "heavy political pressure" from those officials, the union could possibly have won.

"The UAW will absolutely have to try again in Chattanooga," Shaiken said. "The vote was too close not to."

(Reporting by Nick Carey; editing by Sandra Maler and Christian Schmollinger)