Butter consists of churned cream or milk and is rich in saturated and trans fats, while margarine is made with plant-based oils and contains healthier fats. Despite margarine being a ubiquitous alternative to real butter, one state has laws on record that restrict where it can be sold.

Per the Wisconsin State Legislature, it's not permissible to serve "oleomargarine or margarine to students, patients or inmates of any state institutions" unless there is a verifiable medical reason to substitute margarine for butter. Wisconsin was spurred to regulate the use of margarine in the state to protect its dairy industry, and restaurants also fall under margarine restrictions.

These laws have since become slightly altered due to rising health concerns, so schools, jails, and hospitals are free to serve butter substitutes at their discretion. However, the law remains in place for state prisons and restaurants, which can only provide margarine to diners when it's specifically requested.