A group says it's opposing the Children and Family Relationships Bill because it implies there's nothing unique about a mother's love.
The new legislation will allow the adoption of children by married couples or single people, regardless of their sexual orientation.
The Bill has now passed all stages of the Dáil, and will go on to be debated in the Seanad.
Spokesperson for the group Mothers and Fathers Matter, Kate Bopp, says Mother's Day is the perfect opportunity to point out that parents of both sexes are important for a child:
The group's chair is Ray Kinsella, Professor of Banking and Financial Services and Healthcare at the Michael Smurfit School of Business at UCD. David Quinn of the Iona Institute is also a member.