During a federal district court hearing in Washington Monday, attorneys debated the constitutionality of a long-standing U.S. Senate rule taken for granted by many: the filibuster.

Represented by Atlanta lawyer Emmet Bondurant, Common Cause filed suit in May, claiming that the filibuster is unconstitutional in part because it allows for minority rule. The plaintiffs include four members of the House of Representatives and several undocumented people living in the United States who were allegedly denied the path to citizenship by the Senate’s filibuster of the DREAM (Development, Relief and Education for Alien Minors) Act.