State secret ballot initiatives

Four states have passed laws requiring secret ballot elections by workers on unionization. This insurance policy was taken out by republican and business interests last November, even though EFCA was already dead. Now the NLRB has threatened to sue the states unless they agree the laws are unconstitutional and preempted. A few years back, I would have bet this was a slam dunk issue for the NLRB, but the scope of Garmon preemption may not seem as broad for the current Supreme Court. We have already entered a time when serious talk of nullification of federal laws by state officials would raise John C. Calhoun from eternal rest and spin Andrew Jackson a few times in his grave. Can serious talk of narrowing preemption when it serves to undercut federal authority be far off?