Rousseau would argue that people are only obligated to obey the laws when they have agreed to be bound by those laws. If they have not agreed to the "social compact," they are not morally bound to obey the laws.
Rousseau says that we are not obligated to obey the law simply because those who impose it have power. He argues, for example, that a robber with a gun has power, but we clearly have no moral obligation to give the robber our money. The same goes, he says, for government.
We are only obligated when we form a social compact. This happens when we agree to be part of a society. When we do this, we agree to obey its laws. Once we have done this, we are morally obliged to obey.