"Scandal is an attitude or behavior which leads another to do evil. The person who gives scandal becomes his neighbor's tempter. He damages virtue and integrity; he may even draw his brother into spiritual death. Scandal is a grave offense if by deed or omission another is deliberately led into a grave offense."
"Scandal can be provoked by laws or institutions, by fashion or opinion.
"Therefore, they are guilty of scandal who establish laws or structures leading to the decline of morals and the corruption of religious practice, or to 'social conditions that, intentionally or not, make Christian conduct and obedience to the Commandments difficult and practially impossible.'"
Catechism of the Catholic Church ##2284, 2286 (http://www.vatican.va/archive/catechism_lt/p3s2c2a5_lt.htm#II). The quote is from a discourse delivered by Pius XII on 1 June 1941.
"The citizen is obliged in conscience not to follow the directives of the civil authorities when they are contrary to the demands of the moral order, to the fundamental rights of persons or the teachings of the Gospel. Refusing obedience to civil authorities, when their demands are contrary to those of an upright conscience, finds its justification in the distinction between serving God and serving the political community. 'Render therefore to Caesar the things that are Caesar's, and to God the things that are God's.' 'We must obey God rather than men'. . . ."
Catechism of the Catholic Church #2242 (http://www.vatican.va/archive/catechism_lt/p3s2c2a4_lt.htm#V).