A PCI Level 1 Service Provider refers to a business or organization that processes over 300,000 transactions per year and must comply with the strictest level of the Payment Card Industry Data Security Standard (PCI DSS). This standard aims to enhance credit card data security and protect against payment card data theft and fraud. Compliance is validated annually by an external Qualified Security Assessor (QSA) or by a firm-specific Internal Security Assessor (ISA).