Multiple applications running on the same portal server

Environment : EP 7.0 SPS12

We have multiple portal applications running on the same portal with different login page for each application. On one of our employee portal, we want to put a login page link for another portal application running on the same portal which requires a different user ID and password to access that application.

The problem we are encountering is, the login page link we put in our employee portal is bypassing the login page for the other application and using the same session as the employee portal. What can I do to make sure application login page show up when accessing the link from employee portal?

Your help is really appreciated.

Thanks

Bhabesh Patel