Despite increasing efforts to implement legislative gender quotas, many countries still encounter substantial popular opposition to this policy. Previous work cannot explain why opposition to legislative gender quotas persists, particularly among young men, a group believed to be open to diversity. We develop and test a theoretical framework linking group threat to men's attitudes toward legislative gender quotas. While the salience of perceived group threat could trigger men's opposition to legislative gender quotas, we expect that this effect will be more profound among young men due to the heightened degree of economic insecurity experienced by younger generations. Using original survey experiments in South Korea, this study demonstrates the strong influence of group threat in the formation of negative attitudes toward legislative gender quotas among young men. These effects, however, are not mediated by traditional gender norms. Our findings have significant implications for the study of gender and politics and democratic representation.