Hi,
I suppose that the menu item used for the link has an access restricted to registered users. And thus, since you're not logged in, you're redirected to the login form.
The menu item user for a link depends on the "Itemid" parameter in the URL. So you need to make sure that this parameter is in the URL (or that there is an alias used) and that the corresponding menu item's (based on the id of the menu item) access is set to public. Then you won't have that issue.
So it's not really a HikaShop issue as far as I understand, more of a menu item setup issue.