Self-Organization | What happens in case of change of workers' union?

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Under the substitutionary doctrine, the new bargaining agent is not bound by the personal undertakings of the deposed union like the “no strike, no lockout” clause in a CBA which is the personal undertaking of the bargaining agent which negotiated it. Thus in Benguet, it was held by the Supreme Court:

The ‘substitutionary’ doctrine, therefore, cannot be invoked to support the contention that a newly certified collective bargaining agent automatically assumes all the personal undertakings — like the no-strike stipulation here — in the collective bargaining agreement made by the deposed union. When BBWU bound itself and its officers not to strike, it could not have validly bound also all the other rival unions existing in the bargaining units in question. BBWU was the agent of the employees, not of the other unions which possess distinct personalities. To consider UNION contractually bound to the no-strike stipulation would therefore violate the legal maxim that res inter alios acta alios nec prodest nec nocet.
“Of course, UNION, as the newly certified bargaining agent, could always voluntarily assume all the personal undertakings made by the displaced agent. But as the lower court found, there was no showing at all that, prior to the strike, UNION formally adopted the existing CONTRACT as its own and assumed all the liabilities imposed by the same upon BBWU.” (G.R. No. L-24711; April 30, 1968)