Rightly or wrongly, here’s one reason why some major Obama big business 2008 campaign supporters now have reservations about supporting him again. It involves a huge Boeing investment in a new assembly plant in Charleston, South Carolina.

Boeing has spent about $750 million so far in building the 787 Dreamliner plant and has already hired 1,000 workers. The plant is supposed to open in the coming days, but the National Labor Relations Board is threatening to shut it down. NLRB officials say Boeing could be in violation of labor relations laws.

That’s because Boeing employees in Washington state, where the firm is based, are largely union members. Employees in South Carolina are not. Here’s how The Wall Street Journal put it: “At issue is whether Boeing chose South Carolina, a state where unions are weak, to retaliate against union workers in Washington, who have a history of strikes that have disrupted production.”

White House officials insist they are not involved in the dispute, noting that the NLRB is independent.

Still, some of President Obama’s Democratic backers in the business community say the White House should make it clear that Boeing and other U.S. firms have a right to build plants – and create jobs – wherever they feel it makes the most business sense. Some have told me that at least Boeing is not outsourcing the plant in another country – as so many American manufacturing companies have done in recent years.

The whole issue underlines at least to some that Obama and his fellow Democrats are “anti-business” and “pro-union.” They strongly deny that. One thing is clear to me: this story is not going away.