Nine state attorneys general sounded off in a letter to the National Labor Relations Board, calling a complaint it filed against Boeing for opening a production facility in South Carolina an assault on their states' economies.

After receiving a complaint from the International Association of Machinists and Aerospace Workers, the NLRB claims Boeing participated in unfair labor practices by threatening to open new, non-union facilities elsewhere when workers went on strike at the company's Washington state production facility in 2008.

Boeing is slated to open its newest 787 airliner assembly line this summer in South Carolina, a "right-to-work" state, in which employee's can't be forced to join a union to work at unionized plants. In Washington state and the 28 states without "right-to-work" laws, once a majority of workers have opted to join a union, everyone can be required to join and pay dues. That gives labor groups an advantage in organizing.

"This complaint represents an assault upon the constitutional right of free speech, and the ability of our states to create jobs and recruit industry. Your ill-conceived retaliatory action seeks to destroy our citizens' right to work," the letter from the attorneys general reads.

The NLRB complaint attempts to keep Boeing from building 787 airliners in the Palmetto State plant, not shut it down. But the company designed the facility to produce three of those type of airplanes each month.

Some have called the NLRB action unprecedented, and South Carolina officials have expressed anger and fear that it could stymie growth. Attorneys general from Virginia, Nebraska, Texas, Georgia, Florida, Alabama, Arizona and Oklahoma joined South Carolina attorney general Alan Wilson in signing Thursday's letter to voice their concerns that NLRB interference could hinder economic growth in their states too.

"Our states are struggling to emerge from one of the worst economic collapses since the Depression. Your complaint further impairs an economic recovery," the letter says. "Intrusion by the federal bureaucracy on behalf of unions will not create a single new job or put one unemployed person back to work."

But the International Association of Machinists and Aerospace Workers insists its filed the complaint out of legitimate concern that Boeing's new plant is aimed at union busting.

"Boeing's decision to build a 787 assembly line in South Carolina sent a message that Boeing workers would suffer financial harm for exercising their collective bargaining rights," Vice President Rich Michalski said.

Boeing claims it has created 2000 jobs at its Seattle area site since it announced it would build the South Carolina Facility and that the 1,000 new jobs there won't take anything from workers in Washington state.

And the group of attorneys general who sent the letter warn that if it moves forward, the NLRB complaint would financially harm all their states.

"The only justification for the NLRB's unprecedented retaliatory action is to aid union survival," the letter said. "Your action seriously undermines our citizens' right to work as well as their ability to compete globally... We thus call upon you to cease this attack on our right to work, our states' economies, and our jobs."

CLICK HERE FOR THE FULL LETTER (PDF)