Starting from 13.12, Employee Portal supports one website for multiple companies' installations.
https://XXXXXX/EPortal/employee/eelogin.aspx
Employee Portal login to the database that is defined at the initial Catalog in EPortal.Config.
specify the database in URL, e.g.
https://XXXXXX/EPortal/employee/eelogin.aspx?dbname=dbDemo
Employee Portal login the database dbDemo.
dbname is the Application Database Name shown in System Information.
to let the user select which company to log in, specify the URL something like that, e.g.
https://XXXXXX/EPortal/employee/home.aspx
(i.e. replaced eelogin.aspx with home.aspx in the URL of 1)