I wish this were true, but the reality is that there is no "requirement," only a "recommendation" for penance on Friday.
...but it is! From the Canon Law of 1983:
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
In the United States, the Episcopal Conference (the NCCB/USCCB) has allowed (per Can. 1253) the substitution of some other form of penance. Nevertheless, the requirement of some penance remains.