Cooperatives, formally established to enhance social welfare and local economic development, often face pressures that divert them from these foundational goals and lead to their transformation into profit-driven entities that exploit market power. Leveraging an unexpected tax change following a vote of no confidence, we examine the pass-through to retail prices as a test for market power, using data from over 250 cooperatives operating in the Spanish fuel market. Our findings reveal a complete pass-through of the tax increase, deviating from the typical pattern observed among for-profit counterparts, which usually exhibit tax under-shifting, indicative of markup adjustments and mar- ket power exertion. Further descriptive evidence highlights lower prices at cooperative gas station relative to for-profit peers which is consistent with the absence of a markup among them. Our study challenges prevailing assumptions by illustrating cooperatives’ prioritization of consumer welfare over profit maximization, thereby justifying the regulatory advantages they enjoy.