Gun violence is a critical public health problem in the United States, but it is rarely at the top of the public policy agenda. The 2012 mass shooting in Newtown, Connecticut, opened a rare window of opportunity to strengthen firearm policies in the United States. In this study, we examine the American public's exposure to competing arguments for and against federal- and state-level universal background check laws, which would require a background check prior to every firearm sale, in a large sample of national and regional news stories (n = 486) published in the year following the Newtown shooting. Competing messages about background check laws could influence the outcome of policy debates by shifting support and political engagement among key constituencies such as gun owners and conservatives. We found that news media messages in support of universal background checks were fact-based and used rational arguments, and opposing messages often used rights-based frames designed to activate the core values of politically engaged gun owners. Reframing supportive messages about background check policies to align with gun owners' and conservatives' core values could be a promising strategy to increase these groups' willingness to vocalize their support for expanding background checks for firearm sales.