A few Muslim employees perform Jumuah Salaat on the premises where they work.

Answer

The minimum number of persons necessary for the validity of Jumua Salaat is four. One is the Imaam, and three muqtadis (followers) according to the Hanafi Math-hab. Jumuah Salaat will be valid at the workplace only if every Muslim is allowed to attend. If the Jumuah is restricted to only the workers, it will not be valid. The validity of Jumuah depends of the condition of general permission. Any Muslim who wishes to join may not be debarred.