The Occupational Health and Safety Administration (OSHA) enforces electrical safety regulations in the United States. Although OSHA has not adopted and does not mandate NFPA 70E compliance, you can be cited for non-compliance. If you wonder how this could be possible, remember that OSHA's authority to do so stems from the occupational Safety and Health Act in particular Section 5(a)(1) and 29 CFR 1910.2(g).
Section 5(a)(1) "The general Duty Clause" of the Occupational Health and Safety act, states that employers "shall furnish to each of his employees employment and a place of employment which are free from recognized hazards that are causing or are likely to cause death or serious physical harm to his employees". This is the clause most cited by OSHA where unsafe work conditions are found to exist.
Section 29 CFR 1910.2(g) states a "National consensus standard" means any standard or modification thereof which has been adopted and promulgated by a nationally recognized standards-producing organization under procedures whereby it can be determined that persons interested and affected by the scope or provisions of the standard have reached substantial agreement on its adoption". NFPA 70E is considered a national consensus standard and as such, non compliance leaves employers open for citation under this clause if they are found not to be in compliance.