with whom Justice Brennan joins, concurring.
I join the Court’s opinion, but write separately to underscore the narrow grounds on which its decision rests and to emphasize what it is not holding today. In particular, the Court does not reach the issue upon which certiorari was granted: whether a court may refuse to enforce an arbitration award rendered under a collective-bargaining agreement on public policy grounds only when the award itself violates positive law or requires unlawful conduct by the employer. The opinion takes no position on this issue. See ante, at 45, n. 12. Nor do I understand the Court to decide, more generally, in what way, if any, a court’s authority to set aside an arbitration award on public policy grounds differs from its authority, outside the collective-bargaining context, to refuse to enforce a contract on public policy grounds. Those issues are left for another day.
I agree with the Court that the judgment of the Court of Appeals must be reversed, and I summarize what I understand to be the three alternative rationales for the Court’s decision:
1. The Court of Appeals exceeded its authority in concluding that the company’s discharge of Cooper was proper under the collective-bargaining agreement. The Court of Appeals erred in considering evidence that the arbitrator legitimately had excluded from the grievance process, in second-guessing the arbitrator’s factual finding that Cooper had not violated Rule II. 1, and in assessing the appropriate sanction under the agreement. See Steelworkers v. American Mfg. Co., 363 U. S. 564, 567-568 (1960); Steelworkers v. Enterprise Wheel & Car Corp., 363 U. S. 593, 596-597, 599 (1960). Absent its overreaching, the Court of Appeals lacked any basis for disagreeing with the arbitrator’s conclusion that there was not “just cause” for discharging Cooper. See ante, at 39-42.
*472. Even if the Court of Appeals properly considered evidence of marijuana found in Cooper’s car and legitimately found a Rule II. 1 violation, the public policy advanced by the Court of Appeals does not support its decision to set aside the award. The reinstatement of Cooper would not contravene the alleged public policy “against the operation of dangerous machinery by persons under the influence of drugs or alcohol.” 768 F. 2d 739, 743 (CA5 1985). The fact that an employee’s car contains marijuana gleanings does not indicate that the employee uses marijuana on the job or that he operates his machine while under the influence of drugs, let alone that he will report to work in an impaired state in the future. See ante, at 44. Moreover, nothing in the record suggests that the arbitrator’s award, which gives the company the option of placing Cooper in a job equivalent to his old one, would require Cooper to operate hazardous machinery. See ante, at 44-45.
3. The public policy formulated by the Court of Appeals may not properly support a court’s refusal to enforce an otherwise valid arbitration award. In W. R. Grace & Co. v. Rubber Workers, 461 U. S. 757 (1983), we stated that the public policy must be founded on “flaws and legal precedents.’” Id., at 766, quoting Muschany v. United States, 324 U. S. 49, 66 (1945). The Court of Appeals identified no law or legal, precedent that demonstrated an “explicit public policy,” 461 U. S., at 766, against the operation of dangerous machinery by persons under the influence of drugs. Far from being “well defined and dominant,” as W. R. Grace prescribed, the Court of Appeals’ public policy was ascertained merely “from general considerations of supposed public interests.” Ibid. See ante, at 43. I do not understand the Court, by criticizing the company’s public policy formulation, to suggest that proper framing of an alleged public policy under the approach set out in W. R. Grace would be sufficient to justify a court’s refusal to enforce an arbitration award on public policy grounds. Rather, I understand the *48Court to hold that such compliance is merely a necessary step if an award is not to be enforced. See ante, at 44.
It is on this understanding that I join the opinion of the Court.