Every year each member will have a certain number of kilometres that can be claimed as partially tax free. Meaning that it will not be taxed at 100% of the applicable tax rate. This limit is configured within the Application Options, found under Tools > Application Options > Global > Payroll, as shown below:
Any kilometres claimed beyond the threshold configured here will no longer have any tax exemption or changes made. This may lead to the changes in taxation on a member's payslip. If you have any further concerns or your member has not hit this limit, please get in touch with the support team and we can investigate further.