There are hundreds of statutory minimum prices, including gasoline in some states. There are numerous agricultural import restrictions and production quotas. All of these government-sanction market manipulations represent seller collusions against consumers. You say, "Williams, how can that be? The Sherman Antitrust Act gives the U.S. Justice Department and the Federal Trade Commission the power to prosecute and levy fines or imprisonment for price-fixing." You're absolutely right. Price-fixing is illegal, and you will face fines or imprisonment, but with one caveat: unless you get permission from congress or your state legislator. If you get permission, price-fixing becomes legal and it's non-price-fixing that's illegal.
There's a little-appreciated fact about collusions. They have a tendency to break down. Why? Because each party to the collusion is alert to the private gains to be made from cheating on the collusive agreement, such as charging a lower price or producing a larger quantity. Collusions need government enforcement in order to work. Part of the unstated mission of some federal agencies in Washington is the enforcement of collusions. That includes the Departments of Commerce, Agriculture, Justice and Labor. One of the surest ways to detect a seller collusion is to see whether there are statutory minimum prices, import restrictions and production quotas.