In Catholic Moral Theology, the civil law is to be a mirror of the Natural Moral Law. So it should never be in conflict with ‘Catholic’ Law. As such, we are obligated to follow them.
In cases where civil law departs from Natural Law, they are, by definition, unjust laws and we are under no obligation to follow them. In fact, we are to oppose them to the extent that depart from Natural Law ( abortion, contraception, so called gay marriage etc…)
Aquinas described such departures from Natural Law, not a laws at all, but abuse of law.
Brendan this is not my understanding of Aquinas.
Can you reference where you derive this from?
I believe both Aquinas and Augustine, for example, accepted that in a broken world the legalisation of prostitution may be necessary for the temporal common good (the proper domain of civil authority). So there are times when civil law may not reflect natural law but that alone does not make the existence of such a civil law unacceptable to Christians.