A growing body of work suggests that people are sensitive to moral framing in economic games involving prosociality, suggesting that people hold moral preferences for doing the “right thing”. What gives rise to these preferences? Here, we evaluate the explanatory power of a reputation-based account, which proposes that people respond to moral frames because they are motivated to look good in the eyes of others. Across four pre-registered experiments (total N = 9,601), we investigated whether reputational incentives amplify sensitivity to framing effects. Studies 1-3 manipulated (i) whether moral or neutral framing was used to describe a Trade-Off Game (in which participants chose between prioritizing equality or efficiency) and (ii) whether Trade-Off Game choices were observable to a social partner in a subsequent Trust Game. These studies found that observability does not significantly amplify sensitivity to moral framing. Study 4 ruled out the alternative explanation that the observability manipulation from Studies 1-3 is too weak to influence behavior. In Study 4, the same observability manipulation did significantly amplify sensitivity to normative information (about what others see as moral in the Trade-Off Game). Together, these results suggest that moral frames may tap into moral preferences that are relatively deeply internalized, such that the power of moral frames is not strongly enhanced by making the morally-framed behavior observable to others.