Jack, if what you're saying is true, I find it very sad as this is having a very negative impact on all employees. This is throwing discredit on a majority of honnest employees.
However, I feel this letter is the expression of a serious midconduct from management as the employee is being considered as a liar prior to any other sort of consideration. I have been sick twice this year. Once for one day, once for two days. I could not even have started an engine or analysed a met report properly.