(a) Each employer shall post and keep posted in each establishment a poster providing information relating to the job safety and health protection afforded to public employees by the provisions of Labor Law, section 27-a. These posters may be obtained from the New York State Department of Labor, Division of Safety and Health. A poster for each establishment shall be posted in a conspicuous place or places where notices to employees of that establishment are customarily posted, and the employer shall take steps to insure that the posters are not altered, defaced, or covered by other material.