Are 2 Jewish partners allowed to withhold the weekly salary of a 3rd partner for any reason -- even without a Din Torah or settlement of a pending lawsuit or any type of agreed mediation to resolve the issues?

The question is much too broad for a simple answer. In theory, if two partners think the third partner swindeled them and they are recouping their losses, there is at least a case to discuss, but if it is some sort of disciplanary action for not working hard enough it would be hard to justify.