If we hired an employee and informed them they will be paid $0.55 per mile for reimbursement but months later we realized we should have been paying $0.50 per mile. Can we in fact deduct the difference from their pay when it was our mistake? Or do w

If we hired an employee and informed them they will be paid $0.55 per mile for reimbursement but months later we realized we should have been paying $0.50 per mile. Can we in fact deduct the difference from their pay when it was our mistake? Or do we just change the rate from now on?