In England, Scotland and Wales, the Solemnity of Sts. Peter and Paul is a holy day of obligation, while it is not in the United States of America.
In the Roman Catholic Church, June 29 is celebrated as the Solemnity of Sts. Peter and Paul and has been a part of the liturgical calendar since the 3rd or 4th centuries. It is viewed as a foundational feast of the Church, as it features the two of the pillars of the early Church, St. Peter the Apostle and St. Paul the Apostle.
For many centuries this feast was considered a holy day of obligation and still is in various places in the world, such as England, Scotland and Wales.
The 1983 Code of Canon Law lists this day as a holy day of obligation.
Sunday, on which by apostolic tradition the paschal mystery is celebrated, must be observed in the universal Church as the primordial holy day of obligation. The following days must also be observed: the Nativity of our Lord Jesus Christ, the Epiphany, the Ascension, the Body and Blood of Christ, Holy Mary the Mother of God, her Immaculate Conception, her Assumption, Saint Joseph, Saint Peter and Saint Paul the Apostles, and All Saints.Can. 1246 §1.
However, the next line states, “With the prior approval of the Apostolic See, however, the conference of bishops can suppress some of the holy days of obligation or transfer them to a Sunday.”
This is what many bishops around the world did in the past few centuries, including the United States.
One of the reasons for this suppression is because June 29 is not honored as a holiday in the United States, and can create many problems with attending Mass on that day.
Furthermore, there does not exist a strong popular devotion to these saints in the United States when compared to a place like Rome, Italy (where June 29 is a city holiday), or even England.
The Church, in her wisdom, has left the decision to mandate holy days of obligation to the local bishops, trusting that these bishops understand their faithful better and can make appropriate decisions in the local calendar.