Every time a consumer swipes his or her credit card, the credit card company collects a fee. Do most consumers know this? Probably not. That’s because American Express rules prohibit retailers from educating consumers about these fees or giving consumers benefits for using lower-cost cards.

Although retailers are fighting for the right to disclose these fees, credit card companies are determined to keep consumers in the dark.

To change these rules, retailers support a lawsuit that will be argued before the U.S. Supreme Court on Monday. The case, Ohio et al. v. American Express, began when the federal government and 11 states sued American Express, claiming that its rules violate U.S. antitrust laws.

After weeks of testimony and extensive briefing, a federal district court agreed. An appellate court later reversed the decision. Now the final determination will be made by the Supreme Court.

Retailers have been fighting the credit card networks’ unfair rules and anti-competitive practices for decades. The rules the Supreme Court will consider are but one example. They prevent consumers from getting basic information about the true costs of their payment choices, and prevent retailers from offering their own incentives or rewards to consumers who choose lower fee payment options.

Keeping consumers in the dark has allowed the banks and credit card networks to control the rewards they give to select customers while jacking up the fees charged to merchants – fees that are ultimately passed on to every customer in the form of higher prices.

For retailers, the solution is simple: let in the light.

Consumers crave transparency. They want to know the origins of their salmon and their T-shirts. They want to know what chemicals are in their water bottles and the calorie content of their breakfast. They use smartphones to read reviews and to compare prices on products right in the store.

Consumers use this information to make purchasing decisions that best fit their lifestyles and their budgets. Why shouldn’t they be allowed to know how much they’re paying to use their credit cards? Or be given the option at checkout to choose additional benefits for using a less expensive payment option?

The informed consumer is at the core of modern retail.  Empowered consumers increase retail competition, which in turn gives consumers more choices and lower prices.

The absence of similar transparency in the credit card market – because of American Express’s rules – has stifled competition in the payments space. The resulting higher fees increase prices for all consumers whether they pay by card, cash, check, or government benefits.

Transparency is the best way to prevent those with market power from stifling competition and innovation. Amex’s rules are the antithesis of the free market principles retailers embrace.

As the U.S. Supreme Court hears this case, America’s retailers hope the court will strike down American Express’s rules in order to allow transparency, marketplace competition and consumer choice to prevail.