The Transparency in Billing Act of 2023 requires hospitals to use unique identifiers when billing for services provided at off-campus outpatient departments, aiming to make medical billing more transparent for patients and health plans. Under the bill, hospitals must obtain a separate unique health identifier for each off-campus outpatient facility and include it on any claims submitted for services performed there; group health plans and insurers are prohibited from paying claims that lack this identifier. The legislation affects group health plans, health insurance issuers, and hospitals operating off-campus outpatient departments, ultimately impacting patients who receive care at these facilities. The Department of Labor must establish a process for reporting violations within one year of enactment and can impose civil penalties on noncompliant hospitals, ranging from $300 per day for smaller hospitals (30 or fewer beds) to $5,500 per day for larger ones. The billing requirements would take effect for plan years beginning on or after January 1, 2024, with the Secretary of Labor responsible for implementing the law through formal rulemaking.