> Canon 1247: On "Holy days of obligation, the faithful are obliged to participate in the Mass"

> Holy days of obligation are special feast days when Catholics must attend Mass and avoid unnecessary servile work, just as on Sundays. Employers must allow Catholic workers to attend Mass on each holy day or attend the vigil Mass the evening before. To purposely skip Mass on a holy day of obligation without a serious reason is a mortal sin.

> The Catholic Church sets aside these special feast days to commemorate key mysteries and events in the life of the Church. Canon 1246 in the Code of Canon Law establishes 10 days in the universal calendar as holy days of obligation. It also gives bishops the ability to "suppress some of the holy days of obligation or transfer them to a Sunday."

> The U.S. bishops have used Rome's permission to keep the observance on the respective day for the following five holy days of obligation listed in canon 1246: Mary Mother of God on January 1, Mary's Assumption on August 15, All Saints Day on November 1, Mary's Immaculate Conception on December 8 and Christmas Day on December 25. Rome allowed the bishops to transfer the observance of Ascension Thursday to the following Sunday and to downgrade the other holy days listed in canon 1246. The U.S. bishops have also used Rome's permission to transfer the following feasts to Sunday when they fall on a Saturday or Monday: Mother of God, Assumption and All Saints. The only two holy days that are not moved in the United States are the Immaculate Conception and the Birth of Our Lord.