Catholic Social Teaching is included in the Church's moral teachings and is intimately connected to the spiritual, sacramental, and daily life of discipleship. This teaching is rooted in Scripture, both the Old and New Testament, as well as the living tradition of our Church. Pope Leo XIII begins a series of encyclicals beginning with Rerum Nevarum, dated May 15, 1891, which has been continued by successive popes and the conference of bishops to the current day.
These encyclicals are available through the Vatican website, and in print from the United States Conference of Catholic Bishops.
Faithful Citizenship: http://www.usccb.org/issues-and-action/faithful-citizenship/forming-consciences-for-faithful-citizenship-document.cfm