It may be there is lack of clarity on what type of causation is the issue, i.e. legal or medical (see attached ACOEM Guideline). If it is truly the latter, then violation of state workers' compensation regulations for provision of medical care may be raised since the exposure (medical cause) guides the treating occ med physician in treatment, return to work, work restrictions, PPE, and so on. At least in some states, if not all, interfering with medical care is forbidden, not to mention impinging on medical ethics. 

Hope this helps.