Dear

Due to the problems we have been experiencing of late in
obtaining your payment for the goods we have delivered in
accordance with the provisions of our contract of
[date]    , we must inform you that we will not be able to
deliver any more goods to you unless you provide us with
adequate assurance for payment on said goods.

We regret having to withhold further deliveries, but, at
this point in time, we have no other viable alternative.

Please let us know promptly what your decision is in regard
to your willingness to provide us with the adequate assurance
we are requesting.