While the 1983 Code of Canon Law for the Latin Rite of the Catholic Church mandates ten Holy Days of Obligation, the bishops’ conference of each country can reduce that number. In the United States, two of the other four Holy Days of Obligation—Epiphany and Corpus Christi—have been moved to Sunday, while the obligation to attend Mass on the other two days, the Solemnity of Saint Joseph, Husband of the Blessed Virgin Mary, and the Solemnity of Saints Peter and Paul, Apostles, has simply been removed.
In addition, in most dioceses in the United States, the celebration of the Ascension has been transferred to the following Sunday. (For more information, see Is Ascension a Holy Day of Obligation?)