If the whistle-blower acted in concert with even one other coworker, and made it clear to all that their actions were concerted, and the whistleblowing was itse

If the whistle-blower acted in concert with even one other coworker, and made it clear to all that their actions were concerted, and the whistleblowing was itself legal (e.g. not divulging a trade secret for the sole purpose or harming the employer), then the refusal to hire such a worker could be a violation of 8(a)1 of the National Labor Relations Act. But this would be hard to demonstrate in most circumstances.