Concerns about card networks’ merchant fees are about to be reignited by Amazon’s upcoming ban of Visa credit cards issued in the UK. The e-commerce titan has taken issue with Visa’s merchant fees—just like many merchants have had problems with all card networks’ fees in the past—and the squabble will likely draw the attention of regulators, potentially complicating card networks’ and issuers’ business models. And if Amazon is able to extract favorable terms from Visa, other major merchants and groups of smaller merchants could start similar boycotts of any card network, creating opportunities for alternative payment methods to take off.