What does Not legal for sale or use in New York for vehicles with CA emissions?

State: New York
Vehicle: 2000 Ford Focus

I need a new catalytic converter for a 2000 Focus. I am planning on ordering one online (RockAuto) but most of them say "Not legal for sale or use in New York for vehicles with CA emissions".

Any idea what this means? Thanks in advance.

Would you recommended ordering it from another site?

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