First classify the relay's load - is it resistive, tungsten lighting, inductive ballast or an electric motor etc. ? You have to take into account the inrush currents.
There are UL and IEC approvals for relays as a component for use in a product. Not at the NEC level unless it's a device like a motor starter I believe.
Many relays have no formal approvals and a "12A" rating is vague for how long it will last with certain loads or if it's fit for purpose.
Example part to look at is popular T9,
T90 appliance relay approvals. It's current rating varies depending on the load/lifetime.