The German retailing association said it expects that World Cup to contribute $2.6 billion in additional spending. And that's not simply from the estimated 1.5 million visitors who will visit Germany before the tournament ends July 9. Another 1.5 million Germans are expected to visit the 12 cities hosting the tournament's games, too.

German retailers are closely watching the experiment to see whether it pays to stay open later.

KarstadtQuelle AG, one of Europe's largest department store operators, is staying open until 10 p.m. nightly. So far, the extended hours are proving popular with customers shopping not only for soccer shirts, but electronics and even groceries, said Joerg Howe, a spokesman for the Essen-based retailer.

"What is running tremendously well is the fan stores," Howe said.

Karstadt has exclusive rights to sell World Cup-themed merchandise, ranging from pins to T-shirts to caps. On game days, those boutiques routinely run low on merchandise, and fans come in before and after games, sometimes as late as 9 p.m. to pick up a must-have Argentina jersey or Sweden-themed backpack.

If parliament does pass legislation to extend shopping hours, Howe said the company will have a decision to make.

"We will do it if it works in different cities and areas," Howe said. "You have to simply weigh what you're spending for the extra hours on staffing and what you're receiving in the extra income. It all depends on the numbers."