Final answer:
Explicit coordination like price fixing is illegal in the US, while tacit coordination, which involves an implicit understanding among firms, is harder to regulate and prove illegal.
Step-by-step explanation:
Although explicit coordination, such as price fixing, is illegal in the United States, tacit coordination such as "an unspoken understanding" is not. Explicit coordination involves clear, direct communication among firms to fix prices, divide markets, or rig bids, which is a direct violation of antitrust laws.
The United States Department of Justice (DOJ), especially its Antitrust Division, along with the Federal Trade Commission (FTC), enforce these laws to prevent such anti-competitive behavior. However, tacit collusion, which is more subtle and involves an implicit understanding without explicit communication, is much harder to regulate and prove.
This sort of coordination can occur when firms in an industry recognize that competition is fierce and understand that competing on price may lead to reduced profits for all, so they engage in parallel behavior that mimicks what would occur if there was an explicit agreement.