What law was broken?
That would be the National Labor Relations Act. Whether or not they did violate the act is something for the court to decide, but since the NLRB conducted an investigation based upon a complaint by the IAMAW it is my belief that they have a responsibility to sue.
So every time some disgruntled union thugs complain to their toadies in the Obama regime, the government is obligated to sue?
i'm sorry, i originally neglected to say that based off their investigation they believed boeing had violated the law - and i believe that when a regulatory agency finds a company to be in violation of the law they have a responsibility to sue.