Start-up Affiniti, which has received $28 million in two funding rounds, provides unsecured credit cards to owners of small businesses in the US who are members of trade associations.

While the number of independent businesses in many vertical markets are shrinking due to consolidation, those that remain are often outside of the targeted area of more established providers of affinity cards.

Affiniti leverages an association’s brand when marketing. It seeks cardholders among established small businesses, not start-ups. Typically, these are businesses with cash flows that do...