What form of violation applies when eight pharmacies agree to set prices for prescription drugs?

In this scenario, the correct answer highlights that the agreement among eight pharmacies to set prices for prescription drugs constitutes a per se violation for horizontal price fixing. Horizontal price fixing occurs when competitors in the same market agree to set prices rather than allowing the market to determine them. This is considered an antitrust violation because it undermines free competition, leading to higher prices and reduced options for consumers.

The law views horizontal price fixing as inherently harmful to competition and the consumer market, which is why it is categorized as a per se violation. This means that no further justification is needed to prove its illegality; the mere act of price fixing among competitors is enough to be deemed unlawful under antitrust laws, specifically the Sherman Act.

In this case, the pharmacies, which operate in the same market and thus are in competition with one another, colluding to set prices eliminates the natural competitive forces that typically drive prices down and improve consumer choice.

In contrast, other options would either misinterpret the legal framework regarding antitrust laws or incorrectly assess the implications of the pharmacies' actions.