A regional director for the National Labor Relations Board has ruled there is merit to claims Boeing Co. illegally fired five workers who support the International Association of Machinists union at the aerospace giant's 787 Dreamliner campus in North Charleston.

The ruling gives the IAM a preliminary win in its ongoing battle with Boeing over establishing a union presence in South Carolina — a right-to-work state with the nation's lowest percentage of union workers.

The charges will now be heard by an administrative law judge. The IAM is expected to file an injunction calling for the workers' immediate return to their jobs while the case is pending.

Boeing should "immediately reinstate our members, sit down now to negotiate a contract with its flight-line employees ... and get back to the business of working with the IAM and our members to build aircraft," said Robert Martinez, the union's national president.

Boeing downplayed the regional director's rulings, saying "there has been no finding of liability" against the company.

"Much like the initial filing of a lawsuit, all that has occurred is that the regional director has decided that the cases should go to trial," said Boeing spokeswoman Libba Holland.

The rulings include three flight-line inspectors who were fired for purportedly failing to notice a bird strike on an engine following a test flight of a 787-10 for United Airlines. Rich Mester, one of those fired, said Boeing never provided any evidence that a bird strike had occurred, although a company investigator said a feather had been found.

The two other union supporters were fired for allegedly violating Boeing's safety rules. All of the workers say their jobs were, in fact, terminated because of their support for the union.

"Boeing has continuously and systematically ignored the law and trampled on the rights of its own employees in South Carolina," Martinez said, calling the rulings "the critical first step" in what could be a lengthy process to have the workers rehired.

Boeing, however, said the workers' union preference had nothing to do with their terminations.

"Each of the terminated employees was discharged for violating well publicized, longstanding and objectively reasonable safety and conduct policies," Holland said. Those policies include falsifying company records, failing to come to work and walking across an active runway.

In addition to the worker termination cases, the NLRB's regional director ruled in favor of the IAM in three instances where Boeing failed to bargain with the union before imposing disciplinary measures against workers.

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The cases are moving forward as the labor board continues to consider Boeing's appeal of a May 2018 election in which a majority of flight-line workers at the North Charleston plant voted for union representation. Boeing is refusing to acknowledge the union until its appeal is settled.

The union battle that's playing out in North Charleston is seen as an important indicator of organized labor's ability to establish an industrial foothold in the South. The Palmetto State's labor laws hamstring a union's ability to collect dues to support its operations and South Carolina is tied with North Carolina for the fewest union workers at 2.7 percent of the workforce.

The effort to bring a union to the Dreamliner plant has had politicians across the spectrum speaking out. Democrats and Independents, including presidential candidate Bernie Sanders, have called on Boeing to recognize the union and negotiate a contract.

"It is alarming that instead of negotiating with the (union), Boeing has instead pursued a campaign of intimidation against the flight-readiness technicians," Sanders, a U.S. senator from Vermont, said in a letter also signed by other senators and sent to Boeing CEO Dennis Muilenburg.

Republicans have offered support for Boeing, including Gov. Henry McMaster who once called the IAM's presence "about as welcome as a Category 5 hurricane."

"We aren’t going to let out-of-state labor unions ruin the wonderful working environment in our state." McMaster said.

A majority of 176 flight-line workers at the North Charleston plant voted in May 2018 to join the IAM. Boeing claims the union illegally split off a small portion of its workforce to unionize after failing in 2017 to win an election involving all of the North Charleston plant's workers.

A regional director ruled in 2018 that the bargaining unit and vote was proper, setting up Boeing's appeal. The federal labor board has not made a final ruling.

The majority Republican board, which includes two appointees by President Donald Trump, is seen as being pro-employer and has reversed several Obama-era decisions that favored workers.

The IAM represents 600,000 active and retired members in the North American aerospace, defense, airline, manufacturing, transportation, woodworking and other industries. The union already represents about 35,000 Boeing workers across the U.S., most of them in Washington state.

Boeing decided in 2009 to open a manufacturing campus in North Charleston — its first in the South — in part to avoid the union activity that’s common at its West Coast locations, according to news reports.

Boeing builds the 787 Dreamliner commercial plane next to Charleston International Airport. The site is the only place that builds the 787-10, the largest and newest Dreamliner model. It also builds other wide-body Dreamliner variants along with a sister plant in Everett, Wash.

Boeing — one of the Charleston region's largest employers, with about 7,300 workers and contractors — also has North Charleston sites that design and build engine parts, build cabin parts for the Dreamliner and conduct aerospace research.