Although ethics is a good start, it's more than that. It's a case of ethics, morality and the law.
If they didn't all match neatly and you had to choose one over the other which would you pic?
You're right. They don't always "match neatly".
Ethics are the beliefs and practices of a culture, society or organization. One could talk about the "ethics" of the Canadian airborne regiment in Somalia in 1994, for example.
Morality is an individual's, organization's, culture's and civilization's beliefs, practices and actions concerning what is deemed to be right or wrong. It can be secular or spiritually based. It can be subjectivist or relativist based or it can be objectivist or universalist based.
The law consists of regulations that organize the conduct of society/societies. They are written and given force by governments, judicial bodies and law enforcement agencies. Laws restrict behavior (backed up by punitive measures) but some laws also empower and protect (human rights laws, animal rights laws, environmental protection laws).
The answer to your question? I agree with remind: I say the law.
Hopefully law and morality are in sync. Hopefully the law is based on universal principles of justice.
Example:
It is wrong (unlawful) to violate a person's/persons' rights and to murder and abuse persons.
If it is wrong/unlawful to violate persons' rights and to commit acts of murder and abuse,
Then it is wrong/unlawful for x to violate z's rights and to commit acts of murder and abuse against z.
If it wrong/unlawful for x to violate z's rights and to commit acts of murder and abuse against z,
Then it is wrong/unlawful for y to violate z's rights and to commit acts of murder and abuse against z.
For any persons you put in place of the variables, it is wrong/unlawful for them to violate human rights and to commit acts of murder and abuse.
Not everyone will agree that the law is synonymous with morality:
Abortion (freedom of choice) laws and laws concerning euthenasia and stem cell research will (often) strenuously be opposed by (some) people, groups and organizations.
When there's conflict between the state or a large corporation and the individual, often the law decides in favor of the state or corporation ("Possession is nine tenths of the law").
Sometimes (subjectivist, relativist) ethics and morality are in agreement with the law, but such a basis of ethics, morality and law is pernicious that they are inacceptable when judged from the perspective of universal principles of justice.
Example:
The ideas of ethics and morality that informed the Nuremberg (nazi) laws in 1930s Germany.