Dear
This letter will confirm [individual's] telephone conversation with you today concerning an increase in our billing rate to [amount] per hour， effective [date] It is necessary that we request this increase due to a rise in the cost of conducting our business. We are faced with an increase in payroll taxes and insurance， along with an increase in our overhead costs. In addition to the above，we also seek a modest profit.
Attached are copies of our service agreement and we request that you sign one copy and return it to us indicating your approval of this new rate.