Only very unjust laws. There is a moral obligation to obey the law even if we don't like it ourselves. We should not pick and choose which laws we want to obey because we don't like them. But if a law is seriously unjust, such as sending Jews to concentration camps, then of course it should be disobeyed. And preferably loudly and publicly, so that your disagreement with the law can be registered.

Where you draw the line, like whether the law is unjust in the first place, can only come from your own internal morality. In the final an analysis, we are each responsible for our own actions (in breaking laws) ind inactions (in acquiescing to bad laws).

I feel we have a moral obligation to work on behalf of justice. That doesn't tell us what to do about an unjust law, it doesn't provide a formula for action. So without being in an actual situation with all of it's messy details, there's no way to know what the expression "working for justice" means in terms of action. As a side note, this answer is general enough to apply to many moral principles: the moral principle only provides a "workshop" which helps you to sort through the problem. It never tells you exactly what to do in a specific situation, because every situation is different. This is why we spend so much time arguing over the details of rules and restrictions -- we forget that values meet action only in individual situations. Generalized rules are wrong much of the time.

I completely agree with ImAlec. I don't feel I need to reiterate anything that he has already so thoroughly put forth. However, there is one thing I think should also be addressed here. In a free, open and democratic society like we find here in the United States, and among other "Western" societies, we are ultimately responsible for the laws that exist. We elect people to represent our needs and values to the various levels of government and they will (hopefully!) give well-educated and careful thought to these issues and make laws based on thoughtful consideration of all relevant information. You can also influence this process through lobbying these representatives. This allows individuals, groups, corporate entities and even other governments to bring their issues before lawmakers hoping to elicit either change in existing laws or the creation of new ones that would be beneficial to their specific needs. There are obvious pitfalls in this system, but it is, by far, the greatest form of governing that we humans have developed yet. While the process of making or changing laws may not always be smooth or without a certain level of controversy, where will always be the availability of change. So, if there are laws that people feel are unjust, the most powerful and responsible way to fulfill any moral obligation you may feel towards these laws is to VOTE. Get involved in the process of how these laws come into being and how they can be changed. That, I feel, is the most important moral obligation we have in a democratic society.

If I can rephrase it, we have a moral obligation not to obey sinful laws. That is considerably more restrictive. I may think that it is a racist, and therefore unjust, law to identify my race on the census form, but I can't point to any commandment that I'd be violating by complying, so I write down my race. But let's say I was in China and despite our best efforts not to, my wife and I conceived an illegal second child. They would have to take us by force to the abortuary; we would not report there on our own two feet, because the one-child-per-couple law is sinful since it requires a nontherapeutic abortion.