Is Catholic teaching against abortion based on natural law?

When the Church uses the term “natural law” it does not mean that which governs the
activities of the material universe, even though there are certainly many natural laws that do just this.

When the Church speaks of a “natural law,” she is referring to a rule of conduct, which God placed in our very nature which enables us to, in some degree, know right from wrong. For example, people automatically know that murder is wrong—regardless of the culture to which they belong. Certainly, people can refuse to acknowledge the messages they receive from natural law and completely blot them out of their consciousness, as in the case of abortion, stealing, masturbation and murder and so on. But down deep they know that such actions are wrong.