Every Catholic who has attained the age of reason, and is not prevented by sickness or other sufficient cause, is obligated to rest from servile work and attend Holy Mass on the following days. In so far as possible they are also to abstain from those labors and business concerns which impede the worship to be rendered to God, the joy which is proper to the Lord’s Day, or the proper relaxation of mind and body. (See Canon 1247)
When the following holy days fall on a Saturday or Monday, the obligation to attend Mass is abolished. They are:
Although the obligation to attend Mass when these three holy days fall on a Saturday or Monday is abolished, parishes are to continue to observe these holy days by scheduling one or more Masses at a convenient time so that people who wish to participate are able to do so.
This was decided at the November 1991 meeting of the National Conference of Catholic Bishops. The action was confirmed by the Congregation for Bishops on July 4, 1992.