As senator, he argued against the Civil Rights Act of 1866. Cowan expressed concern that the first section of the Civil Rights Act of 1866, which repealed "Dred Scott v. Sandford" and granted birthright citizenship to all persons born in the United States, would grant citizenship to Gypsies and Chinese people. Cowan was especially concerned that the law would allow women the right to enter into contracts independently of their husbands. The debates over the Civil Rights Act included guaranteeing, at the federal level, the right for any free person to enter into a contract, and he argued that the federal government was not to involve itself in regulating contract law, which he saw as squarely within the domain of state power. In particular, he argued that the federal guarantee of contract rights might allow women to enter into contracts under their own person and not in the person of and with consent of their husbands. Woman's ability to enter into contracts was illegal due to coverture law, which were the set of laws referred to as the "civil death" of women. Under coverture, women's husbands owned their wives' property, wages, and body. Women had no legal right to contract, to property, or to bodily autonomy. Senator Cowan cautioned against the Civil Rights Act of 1866 as a bill that would threaten this order. According to Senator Cowan, "A married woman in no State that I know of has a right to make contracts generally...Now, I ask Senators...whether they are willing...to interfere with regard to the contracts of married women...I say that this bill...confers upon married women, upon minors, upon idiots, upon lunatics...the right to make and enforce contracts."