Final answer:
Amira and Sujat's agreement not to purchase tires from Tova Tires constitutes a horizontal restraint of trade, as it is a collaboration between competitors to restrict competition with a supplier.
Step-by-step explanation:
If Amira and Sujat, during a family vacation, discuss the change of tire suppliers and make an agreement that neither would purchase tires from Tova Tires, then a conspiracy to restrain trade, specifically a horizontal restraint of trade, has likely occurred.
A horizontal restraint of trade happens when competitors at the same level of the market agree to work together to restrict competition, such as by fixing prices, limiting production, or boycotting a supplier.
In this scenario, Amira and Sujat are engaging in a mutual understanding to not purchase from a specific supplier, hence they are directly collaborating to restrict trade with Tova Tires.
This is distinguished from a vertical restraint of trade, which would involve agreements between different levels of the production and distribution process, such as between manufacturers and retailers.