"I am writing with regard to [Month's] overtime payments to employees in the Maintenance department.
In reviewing the employees' overtime payments, [we – who? Specify] found a number of discrepancies in your overtime calculations which appear to have affected all the employees. Can this be explained by changes you made to the basis for calculating overtime?
If this basis was indeed changed, you should have announced this before making the monthly payments so that we could have avoided having to contact you in this manner.
In addition, please be aware that, upon receipt of the overtime payments, I made enquiries with your accountant because I had doubts about the accuracy of one particular employee's overtime payment. I was told that the payment was correct. However, even if you calculate the payment on the basis of a revised overtime rate there [is clearly][appears to be] a shortfall in the payment made to him.
[Previously, overtime paid to the employees [of our department] was calculated at an hourly rate - ? So it's not calculated at an hourly rate anymore?]. [(normally, hourly rate calculate as daily rate = monthly paid/no. of working days, hourly rate = daily rate/normal hours of work) – I'm not sure of the sense of this. Is this a comment or is this part of the text? If part of the text, please clarify]. Could you clarify why the basis for calculation has changed?"
Hope that helps!

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