The joint employer rule under the National Labor Relations Act determines when a company that uses workers supplied by a staffing agency or contractor can be held responsible for those workers' labor rights alongside the staffing company. A broad standard (favored by labor advocates) means large corporations using contract workforces must bargain with those workers' unions. A narrow standard (favored by employers) shields the primary company from labor liability. The NLRB under the Biden administration adopted a broader standard; the Trump-reconstituted NLRB reinstated a narrower rule in February 2026.