Two experiments tested how environmental policy acceptability of US conservatives and liberals was influenced by manipulating the level (minority vs. majority) and source (in-group vs. outgroup) of normative support for policy. Results from 928 MechanicalTurk users (Study 1: N = 268, Study 2: N = 660) indicated that when evaluating an in-group policy (that participants expect their own political group to support), communicating outgroup support increases acceptability compared with communicating in-group support. The outgroup norm has a positive indirect effect via the inference that the in-group is even more supportive of the policy than the outgroup is. In contrast, when evaluating an outgroup policy, communicating in-group support indirectly yields higher acceptability than communicating outgroup support, via the inference that the outgroup is more supportive than the in-group is. This effect mainly occurred for individuals with strong ideological identification and was independent of level of support (minority vs. majority). Results indicate that bipartisan support for environmental policies can be achieved by strategic communication of normative information about political groups.