Dafydd - Tom has held out the laudable value of "standing by the strength of one's convictions" when he suggests that "the only way that law can be challenged is for someone to break it and have it end up in court. That is one of the great freedoms in our country." It takes integrity to publically hold oneself out in defiance of what is felt to be an unfair or unconstitutional law, because such individual must be prepared to fully bear the consequences of his/her actions if the courts are not persuaded to see the law in question as unfair or unconstitutional.
Now let's consider the act of using the sick leave because you believe you were not treated fairly. Do you say to your principal, "The no-buy-back rule is unfair to individuals who have made a career commitment to the children of our community. Our contract, although negotiated through the union and duly ratified by its members, unfairly benefits one party over the other and as such is unenforceable. So now, in the grand tradition of our Colonial American forefathers (and foremothers, if there indeed is such a word), Mathatma Ghandi, Rosa Parks, and so many others who have, at great personal cost, challenged unust laws, I say to you that your rule is an offense to justice. I am herewith notifying you that, although not in any way ill, I shall be out on sick leave tomorrow and the next day and the next day. And if you, blind to the injustice you are perpetrating, have to take action against me, so be it, because my inaction would otherwise signal acceptance of the injustice and I am prepared to bear the consequences to ensure that future generations will not be saddled with this affront to a civilized way of life" (or something like that)? Or do you just quietly call in sick, cash the paycheck, and privately assure yourself that it fair? If the former approach is employed, I applaud you. But just calling in sick only promotes your personal gain, without ever raising the noble calling that was the putative genesis of this issue.