This transmittal is intended for physicians, providers, and suppliers querying Medicare’s Common Working File (CWF) for checking eligibility and entitlement status for Medicare beneficiaries. Providers, clearinghouses, and/or third-party vendors, herein referred to as “Trading Partners,” verify an individual's Medicare eligibility and entitlement status prior to and/or while the individual is receiving services before billing Medicare for services rendered to Medicare beneficiaries using HIPAA Eligibility Transaction System (HETS) and/or CWF. Within CWF, Trading Partners use CWF Provider Queries, ELGA, ELGH, HIQA, HIQH, and HUQA. Currently, Trading Partners are allowed to use either legacy Provider Numbers (CMS Certification Number (CCN) or Unique Physician Identification Number (UPIN)) or NPI on CWF Provider Queries. CMS is requiring CWF to modify CWF Provider Queries to only accept NPI as a valid Provider Number.