The problem is the one way communication. I would personally have no problem giving out my past salary, in return for the current salaries if all comparable current employees at the company.
You can refuse to answer their question. You can also ask them how much others are making at your position (and they can refuse to answer that, too). I don't see where the asymmetry is.
It doesn't go that far, but this bill does specify that asking about salary history is allowed if at the same time you communicate a proposed salary range.
