[cfqycwz]

Under US law, the only way to gain recognition as the bargaining representative of a unit of employees—and the only way an employer is legally allowed to recognize you as the sole bargaining agent—is by demonstrating that you have the support of a majority of the bargaining unit, usually through a union certification election.

I don't think there's anything legally preventing a subset of employees from banding together and withholding work until just that subset gets what they want, if that's what you're asking. It's just not a terribly effective tactic, and obviously doesn't leave the benefits in place for future employees the way that a NLRB-sanctioned collective bargaining agreement does.