Tom Wroblewski, the district president of the International Association of Machinists and Aerospace Workers union, which filed the initial complaint with the NLRB, said the issue had been high-jacked by conservative politicians.
"Partisan politics, particularly on the right, have seized upon the issue and are spinning it to fit their broader anti-union or anti-Obama agendas," he wrote in a letter to Boeing employees at the new South Carolina plant.
While Boeing spokesman Sean McCormack would not comment on the case's political ramifications, he said the lawsuit raises questions about the ability of companies to make decisions about where they do business.
"Here you have a major American manufacturing company, Boeing, making a billion-dollar investment on manufacturing capacity in the U.S.," McCormack said. "We think that should be celebrated. Instead, we have a threat from the government, more specifically from the NLRB, to call for a remedy that would effectively close the plant."
The NLRB case began Tuesday with a hearing in Seattle and is expected to last a couple of weeks, the board spokesman said.
McCormack said Boeing does not expect to win the case in front of the labor board and will appeal to the U.S. Circuit Court.
"We believe that the complaint is a frivolous campaign not grounded in law and runs contrary not only to NLRB precedent," McCormack said, "but also established Supreme Court precedent."