If your business takes American Express cards, you'll be interested in the federal court case now unfolding in U.S. District Court in Brooklyn, New York, against the financial services giant. You could emerge the winner, with potentially greater flexibility regarding which cards your customers use.

Here's the deal: AmEx has been charged with anti-competitive practices by the Department of Justice, which alleges that the card company's bylaws burden merchants who accept the company's cards. In someting called "anti-steering" rules, the company forbids merchants from guiding customers to pay with less costly cards, such as MasterCard and Visa.

At issue is whether the card company is sufficiently large enough to consitute a monopoly. American Express says it has 55 million cards in in the U.S., and only 3 million merchants that accept it. That's a fraction of the nealry 300 million cards Visa has in circulation in the U.S., and the nearly 200 million MasterCard has.

But federal prosecutors say that's big enough for them. On Tuesday in court, according to Bloomberg, Craig W. Conrath, a DOJ lawyer, told Judge Nicholas Garaufis: “AmEx does not have to worry that a competitor is going to come along with a lower price.”

American Express has some of the highest interchange fees in the credit card industry. Interchange fees are what card companies charge merchants to accept their cards from consumers. The fees can be vastly different depending on the type of card and the brand. For example, rewards cards can carry higher fees than standard credit credit cards. (Some businesses, however, can negotiate on rates, depending on how much credit card volume they process.)

AmEx's interchange fees on average are 3.5 percent, compared to 2 percent for MasterCard and Visa.

MasterCard and Visa were both the subject of the largest class action in history over claims of price fixing for their own interchange fees. That case was settled in 2012, with the card companies agreeing to return more than $7 billion to merchants.