Lockheed Martin stated that they would follow the law; but based on new information (provided by the DoD) the WARN notices aren't required at this time because the layoffs wouldn't happen right on January 2nd. Any sequestration layoffs wouldn't happen until a few months later and so notices aren't required until 60 days (or 90 depending on the state) before the actual layoffs.
They avoided legal trouble because they are following the law and, at the same time, avoided becoming a political target by not sending out the notices. And, best of all, they still got their message out to their employees and the voting public that sequestration will lead to massive layoffs. Win-win-win.