Morally charged rhetoric is commonplace in political discourse on immigration but scholars have not examined how it affects divisions over the issue among the public. To address this gap, we employ preregistered survey experiments in two countries where anti-immigration rhetoric has been prominent: the United States and Denmark. We demonstrate that exposure to moralized messages leads respondents to place greater moral weight on their existing immigration opinions and become more averse to political leaders and, in the United States, social interaction partners who espouse opposite beliefs. This suggests that political moralization contributes to moral conflict and affective polarization. We find no evidence, however, that moral framing produces attitudinal polarization—that is, more extreme immigration opinions. Our study helps make sense of the heightened intensity of anti-immigrant politics even when attitudes are stable. It also suggests a promising avenue for comparative research on affective polarization by shifting the focus from partisanship to the moralization of existing issue disagreements.