I'm far from an expert here, so I'm most likely incorrect in what I'm about to say.
I would think going the CCMA / Not signing / finding a legal way to prevent the salary reduction would end up in more time wasted and a lot of frustration when you hit a dead end. Chances are the company can prove things are bad and that would be enough for the law / CCMA to side with them.
I'd rather focus my energy on finding something better, and contact a whole whack of recruiters to do so.
If a company is doing that, it's a clear sign to leave, not to try find ways to prevent it. It's all very easy for me to say all this now, but I'd like to think I'd go with what I have said if it happened to me.