A health insurer and a benefits services form are teaming up to market post-retirement health coverage programs to large employers.

A unit of UnitedHealth Group Inc., Minnetonka, Minn. (NYSE:UNH), and Towers Watson Inc., New York, say their new Retiree Health Collaborative will serve Medicare-eligible retirees and early retirees at employers with 500 or more retired plan participants.

The collaborative started serving 7 pilot clients in late 2009; those clients have a total of about 25,000 retirees.