The NLRB is not structured or mandated anything like a prosector's office. They're an administrative board which does arbitration; their relationship to a legal court is essentially that of a lower court to a higher court. A prosecutor's office has a mandate to prosecute; the NLRB has a mandate to evaluate evidence on all sides of a labor-centric legal issue and offer a non-legally-binding judgment.

True, but it needs the courts to enforce any decision - that's the arbitration of guilt or innocence, not just the NRLB saying violations occurred. An NRLB finding is more like a grand jury deciding to indict - a level of evidence has been met, but the bar is pretty low.

If a violation is believed to exist, the region will take the case before an Administrative Law Judge who will conduct a hearing. The decision of the Administrative Law Judge may be reviewed by the five member Board. Board decisions are reviewable by United States Courts of Appeals. The Board's decisions are not self-executing: it must seek court enforcement in order to force a recalcitrant party to comply with its orders.

https://en.wikipedia.org/wiki/National_Labor_Relations_Board...