With reference to your request to delay delivery until …, I am compelled to inform you that your proposal is not acceptable to us.
I am sorry to have to decline your request for postponement of delivery.
In view of our commitments and long-term contracts, we are unfortunately not able to concur with your request.
If you fail to comply with the terms of our contract, we will have no option but to / be forced to recover expenses from you.
We are sorry to inform you that we are claiming damages for late delivery of …
We must insist that you indicate your reaction to this proposal prior to Monday 10.00 Eastern Standard Time.
I feel confident that a mutually agreeable solution can be worked out.
We will consent to a delay of seven days at the most if you are willing to grant a 5% reduction in the regular price.
Due to greater flexibility in next month's scheduled production, the second consignment may possibly be despatched ten days later.