By definition, if a law is unjust, then following it is immoral (that's all it can mean for a law to be unjust) and thus disobeying it is not just morally licit, but morally required.
But that's missing the real issue. It's all well and good to talk of a hypothetical, theoretical "unjust law", but this premise assumes perfect moral knowledge on the part of the individual. Real individuals, of course, fall short of that. Moral error is a universal fact of human nature, I'm sure even atheists concede as much. So the real question isn't "is it right to break an unjust law?" but "is it right to break a law that I (possibly mistakenly) feel is unjust?"
There are many factors to consider in answering that question, of course. The most important is who made that law. If you live in a democracy, then the presumption is that a majority of the citizenry believed the law to be just (obviously the gap between the ideal democracy and the very flawed reality we see is quite big, but that's a question for another day). And if a majority believed so, then I'd say that in almost all circumstances the right thing to do is to defer to one's peers. Who the hell are you to say the majority is wrong? Of course there are exceptions, but they are rare and should be fully motivated.
If laws are passed by citizens referenda perhaps you could argue that. But in parliamentary democracies it's a big jump to take an individual elected members vote, which may be for political or personal moral reasons, then pooled together to enact a law, as representative of majority opinion.
