Catholics are obliged to obey Canon Law under pain of sin. The following are canons, which concern Friday, the day on which our Lord Jesus Christ died. They might surprise you.
Can. 1250: The days and times of penance for the universal Church are each Friday of the whole year and the season of Lent.
Can. 1251: Abstinence from meat, or from some other food as determined by the Episcopal Conference, is to be observed on all Fridays, unless a solemnity should fall on a Friday. Abstinence and fasting are to be observed on Ash Wednesday and Good Friday.
Can. 1253 The Episcopal Conference can determine more particular ways in which fasting and abstinence are to be observed. In place of abstinence or fasting it can substitute, in whole or in part, other forms of penance, especially works of charity and exercises of piety.
(Taken from: http://www.intratext.com/IXT/ENG0017/_P4M.HTM)
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