Noting that when motivation of employer in taking certain action is at issue, "[the General Counsel's] refusal to elicit th[e] readily available and crucial testimony of a disinterested witness may well be taken to mean that the information was adverse to his case."
Holding that an employer was not entitled to a rehearing before the Board concerning a violation found by the ALJ that had not been charged in the complaint and that had not been considered or argued by either party