The main purpose of the proposed legislation, known as the Stop Aid for Foreign Expulsion Act or SAFE Act, is to prevent the use of federal funds to pay foreign governments or entities for the detention of individuals if a U.S. court has ruled that such detention is unlawful under U.S. law. This aims to ensure that American taxpayer money is not used to support or facilitate actions that violate U.S. legal standards regarding individual rights and detentions.