Day of Prayer for the Legal Protection of Unborn Children - January 22
The General Instruction of the Roman Missal (GIRM), no. 373, designates January 22 as a particular day of prayer and penance for abortion, called the "Day of Prayer for the Legal Protection of Unborn Children."
Full relevant section from the GIRM:
“373. Masses for Various Needs and Occasions are used in certain situations either as occasion arises or at fixed times.
Days or periods of prayer for the fruits of the earth, prayer for human rights and equality, prayer for world justice and peace, and penitential observances outside Lent are to be observed in the Dioceses of the United States of America at times to be designated by the Diocesan Bishop.
In all the Dioceses of the United States of America, January 22 (or January 23, when January 22 falls on a Sunday) shall be observed as a particular day of prayer for the full restoration of the legal guarantee of the right to life and of penance for violations to the dignity of the human person committed through acts of abortion. The liturgical celebrations for this day may be the "Mass For Giving Thanks to God for the Gift of Human Life” (no. 48/1 of the Masses and Prayers for Various Needs and Occasions), celebrated with white vestments, or the Mass “For the Preservation of Peace and Justice” (no. 30 of the Masses and Prayers for Various Needs and Occasions), celebrated with violet vestments.”