How consistent do they have to be? Law abounds in absolute-sounding formulations that are never interpreted absolutely in practice. By policy (though probably not by law) my company has a consistent salary scale across the company. There are hundreds of people of my position and rank, managed by dozens of managers, many of whom have never met each other. (Yes, my company is really that epically huge.)

Is a Software Engineer B in my group exactly the same as a Software Engineer B in every other group in the company? Of course not; a pay grade is just a vague description interpreted by many different managers from diverse backgrounds. Yet people are content to say that we have a consistent pay scale.

The union would fight against it because they oppose giving any discretion to management, but teachers might defect from the union if it meant a chance at making teaching a rewarding and respected profession.