"The notice must be posted prominently, where it can be readily seen by employees and applicants for employment."
"The poster must be displayed in a conspicuous place where employees and applicants for employment can see it."
Found the above verbiage on US DOL website in reference to required labor law posters and their display. From that, I would say you would not have to have one on each floor as long as you had one that can be seen by all employees/applicants.
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Life is the willingness to be yourself and live in harmony with others. - Dr. Cherie Carter-Scott