Union workers at a Boeing plant in Washington state went on strike in 2008.

So not surprisingly, when Boeing set up a second assembly line to build some of its new 787s, it chose its non-unionized plant near Charleston, S.C.

But now, the National Labor Relations Board has filed a complaint against Boeing over its decision to assemble 787s in South Carolina.

The federal agency says, in effect, that putting the new assembly line in an area beyond the reach of the International Association of Machinists and Aerospace Workers union is "discriminating based on union activity," The Associated Press reported recently. The NLRB says that amounts to "retaliation" against the union for the 2008 strike in Washington.

But punishing Boeing for building outside a union-controlled area more or less sets up a protection racket for Big Labor.

Private-sector unions may have a right to strike, but exercising that right creates big costs for the companies that employ the unions' members. It is perfectly natural that companies that have been hit with such costs would think twice before expanding operations in union-dominated areas. The federal government should not punish them for that.