How can you show your opposition to what you consider an unjust law

Many people create a petition to explain why they consider this law unjust and find a collection of people that feel the same way and present it to the proper authority, usually a judge or the Supreme Court, and petition to review a law or abolish a law.

FOR example if a white person and a black person were in line for an iphone 7 and they said there were no more and they gave the white person one after they said there were no more sorry if this isn't a good example