The nation's largest pro-business lobbying group Friday denounced the National Labor Relations Board lawsuit that seeks, in effect, to shut down Boeing Co.'s $750 million North Charleston assembly plant.

The U.S. Chamber of Commerce, which represents about 3 million employers, joined the growing chorus of Boeing defenders by issuing a written statement.

"We would rarely comment on the merits of a case still in its earliest stages. However, the precedent that the NLRB is attempting to establish here is so fundamentally unsound and troublesome that it cannot be ignored," said Randy Johnson, senior vice president for labor, immigration and employee benefits.

The federal labor agency sued Boeing on Wednesday, alleging that it set up its 787 Dreamliner production plant in North Charleston partly to retaliate against the International Association of Machinists and Aerospace Workers for past strikes in Washington state.

The labor board said Boeing executives told unionized employees that the company would move or had moved production work away from the Puget Sound area partly "to retaliate for past strikes and chill future strike activity."

NLRB acting general counsel Lafe Solomon said that violates the National Labor Relations Act.

Boeing and its supporters this week said the expansion was based on numerous factors. The U.S. Chamber said that the company considered "a wide variety of legitimate business-related reasons allowing it to meet the demands of its customers and therefore, to remain competitive."

Solomon said the NLRB recognizes the rights of employers "to make business decisions based on their economic interests, but they must do so within the law."

The lawsuit seeks an order forcing Boeing to establish its secondary 787 factory in Everett, Wash., the unionized site of the primary Dreamliner assembly line.

The aerospace giant's local production workers are not represented by the IAMAW.

Boeing said this week that it will fight the lawsuit, and it called the allegations frivolous. It also said its North Charleston plant would open on schedule this July.

The company already has hired about 1,000 of the estimated 3,800 employees it will need to staff the new line, which is designed to produce three 787s a month.

The lawsuit will be taken up by an NLRB judge at a June 14 hearing in Seattle, the start of what labor experts predict will be a long and costly legal battle.