From Pope St. John Paul II’s Apostolic Exhortation Familiaris Consortio (1981):
There are increasing cases of Catholics who for ideological or practical reasons, prefer to contract a merely civil marriage, and who reject or at least defer religious marriage. Their situation cannot of course be likened to that of people simply living together without any bond at all, because in the present case there is at least a certain commitment to a properly-defined and probably stable state of life, even though the possibility of a future divorce is often present in the minds of those entering a civil marriage. By seeking public recognition of their bond on the part of the State, such couples show that they are ready to accept not only its advantages but also its obligations. Nevertheless, not even this situation is acceptable to the Church.
The aim of pastoral action will be to make these people understand the need for consistency between their choice of life and the faith that they profess, and to try to do everything possible to induce them to regularize their situation in the light of Christian principle. While treating them with great charity and bringing them into the life of the respective communities, the pastors of the Church will regrettably not be able to admit them to the sacraments.
— Familiaris Consortio 82