An employer lost its case before the NLRB, at a time when it was questionable whether the Board had a quorum. The employer then sought review at the 8th Circuit, and argued that the Board's order was unlawful for lack of a quorum. One big problem. Or really two big problems. The employer did not raise this issue at the level of the NLRB, and did not raise the issue in its initial brief at the Court of Appeals.
Result: The issue was waived. The employer lost. NLRB v. RELCO Locomotives (8th Cir 08/20/2013).
Meanwhile, the US Supreme Court has this issue on its docket. NLRB v. Noel Canning. Briefing should be completed by late November. Oral arguments have not yet been scheduled.