You do not need a referral letter from MOM to engage a DWD or service provider to conduct audiometric examinations for your employees. Your company may engage a service provider from MOM's published list of industrial audiometric examination service providers. These providers are familiar with MOM's requirements and will help ensure your compliance professionally.
Under the Workplace Safety and Health (Medical Examinations) Regulations, it is the duty of the employer to ensure that their employees who are exposed to excessive noise undergo pre-placement and periodic medical examinations by a Designated Workplace Doctors (DWD).