Can I use an array with fields_for ?

Ok, I'll try one more time...I've read the book, I've searched the docs, I can't find the answer this puzzle.
Surely someone can help!

@rs is an array, and I want to have a select field for each item in @rs.
How can I do this? The following (which is inside a form_for) does not work:

    <% for r in @rs %>
    <% fields_for r do |f| %>
       Employee: <%= f.select (:employee_id, ['alan', 'bob'] %><br/>
    <% end %>

I get the error
'@#<AccountEmployeeRelation:0xb7628038>' is not allowed as an instance
(each item in @rs is an AccountEmployeeRelation)