Nearly seven years after a landmark overhaul of the credit card industry, regulators are renewing their scrutiny of a popular type of loan that can pack a big punch for consumers who don’t use it as intended.

Deferred-interest promotions, commonly offered on store-brand credit cards, give consumers a chance to buy big-ticket items like appliances and furniture and put off paying interest for the first six months to a year. Richard Cordray, the head of the Consumer Financial Protection Bureau (CFPB), told Congress that regulators had significant concerns about the promotions. The agency issued a report that said the number of purchases made on these promotions increased 21 percent between 2010 and 2013.

Alan Kaplinsky, who leads Ballard Spahr’s Consumer Financial Services Group, said that many bank issuers had already brought their disclosures involving deferred interest into compliance, although it hasn’t always been easy without a formal rule in place.

"It’s taken a while for the industry to figure out what the CFPB’s expectations were," said Mr. Kaplinsky. "If they find an issuer they think is hiding the ball about how these promotional offers work, there’s no question in my mind that they’ll certainly go after that credit card issuer."