PCI DSS has different compliance requirements for different levels of merchant processing transactions.
Level 1: >6 million annual card transactions
Level 2: 1 to 6 million annual card transactions
Level 3:  20K to 1 million annual transactions
Level 4:  <20K annual transactions
You may also be required to have an elevated level of compliance if you’ve had a data breach or if your payment processing structure could pose an information risk.