bargaining obligations, the courts and the NLRB have developed two conceptually related, but distinct theories — “single employer” and “alter ego” — to guard against such abuse. Carpenters’ Local Union No. 1178 v. Stevens, 743 F.2d 1271, 1275-77 (9th Cir. 1984), cert. denied, 471 U.S. 1015, 105 S.Ct. 2018, 85 L.Ed.2d 300 (1985).
The requirements of these two theories overlap substantially. Under both theories, the district court must first determine whether the two firms are a single employer by measuring the degree of common ownership, management, operations, and labor relations. See id. at 1276. If this threshold requirement is met, the next step depends on which theory is pursued.
Under the “single employer” theory, the district court must defer to the NLRB, which has primary jurisdiction to determine whether the employees of both the union and non-union firms constitute an appropriate bargaining unit. Only if the NLRB finds that they constitute a single unit may the collective bargaining agreement with the union firm be extended to the non-union firm. See South Prairie Constr. Co. v. Local No. 627, Int’l Union of Operating Eng’rs, 425 U.S. 800, 805-06, 96 S.Ct. 1842, 1844-45, 48 L.Ed.2d 382 (1976) (per curiam); Carpenters’ Local Union No. 1478, 743 F.2d at 1276-77 n. 7; N.L.R.B. v. Don Burgess Constr. Corp., 596 F.2d 378, 386 (9th Cir.), cert. denied, 444 U.S. 940, 100 S.Ct. 293, 62 L.Ed.2d 306 (1979). This is because the fact that Nor-Cal and North Bay may constitute a single employer does not necessarily mean that their employees share a “community of interests” sufficient to make them a single bargaining unit. See Don Burgess, 596 F.2d at 386. This bargaining unit issue, which is a representational question, must be decided by the NLRB in the first instance. See 29 U.S.C. § 159(b) (“The Board shall decide in each case ... [what] the unit appropriate for the purposes of collective bargaining shall be_”); Carpenters’ Local Union No. 1478, 743 F.2d at 1278; Cappa v. Wiseman, 659 F.2d 957, 959 (9th Cir.1981).
Accordingly, if appellees had relied solely on the “single employer” theory, appellants would have prevailed on their primary jurisdiction argument. The district court could not have, extended the collective bargaining agreement to North Bay without a prior determination by the NLRB that the employees and North Bay and Nor-Cal constituted a single bargaining unit.
But appellees bypassed the “single employer” theory and instead invoked the “alter ego” theory. To prevail on the “alter ego” theory, appellees were required not only to make the threshold showing that the two firms were a single employer, but also to prove that North Bay was being used “in a sham effort to avoid collective bargaining obligations,” Brick Masons Pension Trust v. Industrial Fence & Supply, Inc., 839 F.2d 1333, 1336 (9th Cir.1988), rather than for the pursuit of legitimate business objectives untainted by “union animus,” Haley & Haley, Inc. v. NLRB, 880 F.2d 1147, 1150 (9th Cir. 1989) (per curiam). See also A. Dariano & Sons, Inc. v. District Council of Painters No. 33, 869 F.2d 514, 519 (9th Cir.1989) (“In all alter ego determinations an element of fraud or misrepresentation also exists.”). It is the settled law of our circuit that once appellees prevailed on these issues, the district court could hold that the Nor-Cal bargaining agreement covered North Bay without first getting a unit determination from the NLRB. See, e.g., Northwest Adm’rs, Inc. v. Con Iverson Trucking, Inc., 749 F.2d 1338, 1340 (9th Cir.1984); Carpenters’ Local Union No. 1478, 743 F.2d at 1276-77 (“[A] showing [that employees óf both companies constitute a single bargaining unit] is not required under the alter ego doctrine.”).2
Relying on Laborers Health & Welfare Trust Fund v. Advanced Lightweight Concrete Co., 484 U.S. 539, 108 S.Ct. 830, 98
2
. Appellants rely on United Ass'n of Journeymen & Apprentices, Local 342 v. Valley Eng’rs, 975 F.2d 611 (9th Cir. 1992), to argue that the primary jurisdiction doctrine also applies in an "alter ego” case. In Valley Engineers, the NLRB made a determination that the two firms were neither a single employer nor alter egos. See id. at 613. The holding in Valley Engineers that the union could not collaterally attack this NLRB determination, see id. at 615, has no application to the case at bar because in this casé, the NLRB has made no determination whatsoever.