But sure, if you want, there are plenty of ways. Mandatory bonuses for higher-risk or generally physical labour would be one easy start, although it likely wouldn't be as effective in practice as one would like it to be. Restructuring the way people are paid as a whole is a more effective solution, which could cover other aspects too, although it would obviously be less popular with The Shareholders™ and therefore more difficult to pass. It's all a matter of legislation - every sane country has a law that says what the salary may or may not be based on, various limits (e.g. minimum wage), bonuses and modifiers... Maybe take inspiration from some countries' public sectors and make salaries fully standardized with a big lookup table and a bunch of modifiers based on objective or at least measurable parameters?