The Secretary of Labor (Secretary) petitions for review, pursuant to 29 U.S.C. §§ 660(a), (b), of the December 6, 1984, final order of the Occupational Safety and Health Review Commission (Commission) suppressing all evidence obtained through two search warrants. An Administrative Law Judge (AU) held these warrants invalid because they were overbroad and consequently violated Cerro’s fourth amendment right against unreasonable searches. Reviewing the petition before us, we reverse the Commission’s order.

A.

On January 2, 1985, this court reversed the district court’s decision which had quashed two warrants obtained by the Occupational Safety and Health Agency (OSHA) for full scope wall-to-wall safety and health inspections of the Cerro workplace in Sauget, Illinois. We remanded the action with directions to approve these warrants. In re Establishment Inspection of Cerro Copper Products, 752 F.2d 280, 284 (7th Cir. 1985) (per curiam). Two days after our decision, the court received a Circuit Rule 11 communication from Cerro with an attached decision of the Commission. The Commission declined to review the opinion of an AU’s holding that OSHA’s search of Cerro had violated Cerro’s fourth amendment rights and thus suppressed all evidence which pertained to any alleged violation other than two initial employee complaint items. 1 In a supplemental opinion, this court held that the decision of the Commission did not in any way affect our opinion reversing the district court, and we remained convinced that the warrants for full scope wall-to-wall searches should still be issued. In re Establishment Inspection of Cerro Copper Products, 752 F.2d at 284.

In this petition, the Secretary asks us to review the Commission’s order vacating the citation issued by OSHA as a result of the inspection conducted pursuant to the challenged warrant. While we acknowledge the maxim that agency orders should not be set aside if supported by substantial evidence, NLRB v. Harvstone Manufacturing Corp., 785 F.2d 570, 574 (7th Cir. 1986), it is clear that this Commission’s decision should be reversed under the doctrine of res judicata, the elements of which we discussed recently in Cannon v. Loyola University of Chicago, 784 F.2d 777, 779 (7th Cir. 1986). Res judicata is designed to prevent parties from relitigating issues that have already been decided. We upheld the validity of the identical warrant involved in the administrative case on this appeal in Cerro, supra, and we see no reason to alter this decision now.

-Besides raising issues it did not raise before the AU, 2 Cerro fails to adequately contest the Secretary’s arguments regarding the application of res judicata. Instead, Cerro provides this court with merit-less contentions. 3 Because (1) the parties to this suit are the same as those in Cerro, *27 supra, (2) this suit alleges the identical cause of action as in Cerro, supra, (3) and we entered a valid final judgment on the merits in Cerro, supra, see Federated Department Stores v. Moitie, 452 U.S. 394, 398, 101 S.Ct. 2424, 2427-28, 69 L.Ed.2d 103 (1981) (requirements for res judicata), this court reverses the Commission’s decision and again remands with directions to approve the safety and health inspection warrants.

Reversed and Remanded.