Employers are required to follow the General Duty Clause of the OSH Act, which requires them to provide workers with a safe workplace that does not have any known hazards that cause or are likely to cause death or serious injury.
OSHA has a number of guidance documents that employers can use to assist them in hazard recognition, detection, control and clean-up of mold. In general the best way to control mold is to identify and control the source or sources of moisture. Once the employer controls the source or sources of moisture, they can ensure the mold-bearing material can either be cleaned or removed. For further information on this subject, see OSHA's Molds Safety and Health Topics page.