Federal OSHA does not specifically require discipline for an employee who violates company safety rules or OSHA regulations. That said, OSHA does seem to encourage disciplinary enforcement of employee safety violations through programs like VPP. 

Some states have their own safety and health laws and enforcement agencies that may have a requirement for disciplinary action, and you should verify that in the state at issue. Also, state workers compensation laws may have a penalty (reduction of benefits) for employees who are injured as a result of violating a known, posted safety rule. This varies from state to state.