German prosecutors have expanded an ongoing investigation of international tax-avoidance deals to cover questionable trades exposed last week by ProPublica and other media partners.

Handelsblatt, which collaborated on the report along with German public broadcaster ARD, reported that Commerzbank is the target of the new inquiry for its involvement in the trades, which cost German taxpayers $1 billion a year in forgone revenues.

The Frankfurt general prosecutor’s office confirmed that it had opened a new investigation but declined to name the target. A Bloomberg report also named Commerzbank as the target.

Commerzbank declined to comment. In an interview with Germany’s Bild newspaper, however, board member Michael Reuther said on Wednesday the trades were “no longer socially accepted” and that the bank will exit the business in Germany and elsewhere ahead of a government move to extinguish them.

Alexander Badle, a spokesman for the Frankfurt prosecutor’s office, declined to provide further details, saying that individuals, rather than corporations, may end up becoming the focus of any of its investigations.

The center of Germany’s finance industry is in Frankfurt, where state prosecutors had previously set up a special unit to pursue criminal investigations into an earlier scandal involving duplicate claims for dividend tax refunds. With the newest probe, Frankfurt now has five open investigations, the spokesman said. Other states also have begun inquiries.

The investigations all center on complex transactions engineered by banks to help international investors avoid paying taxes on dividends they receive from German companies.

In the deals, known broadly as “dividend arbitrage,” foreign investors briefly lend their shares of German stocks to German banks or funds that can claim a refund of dividend taxes that are withheld. The loans bracket the stock’s dividend record date; participants split the tax savings. (See how it works and the annual spikes in borrowing DAX 30 shares.)

One variety of dividend arbitrage – known as “cum/ex” trades – was engineered to help investors and banks reclaim more tax money than was actually withheld by the government. These deals were outlawed by Germany in 2012, and more than 100 banks are under investigation by German tax authorities, Handelsblatt has previously reported.

But confidential documents obtained by ProPublica showed that bankers have continued to book other dividend arbitrage deals, known as “cum/cum.” In these trades, only one tax refund is claimed for each share receiving dividend payments. Those transactions are now also the focus of the Frankfurt prosecutor’s expanded investigation, the spokesman confirmed.

ProPublica estimated the loss from these trades at $1 billion a year to the German treasury. Documents indicate that at least 20 other countries are active markets for this type of dividend arbitrage.

Commerzbank played a key role in enabling the tax-avoidance by signing on as borrower of the shares. That struck a raw nerve in Germany, where taxpayers rescued the bank from failure during the 2008 financial crisis with a $21 billion bailout.

Leaders of the opposition in Germany’s Parliament invited Finance Minister Wolfgang Schäuble and Commerzbank Chairman Martin Zielke to discuss the deals today. Neither accepted the invitation, however, because leaders of the ruling party voted against the discussion and moved it to a special committee where any meetings will be held in secrecy.

Schäuble’s Finance Ministry has proposed legislation to eliminate dividend arbitrage transactions, but lawmakers have yet to vote on the measure. A hearing on the proposed reform was held on Monday; another hearing is scheduled in July.

This article was written by Cezary Podkul, with reporting contributed by Arne Meyer-Fünffinger of Bayerischer Rundfunk in Berlin and staff of the Handelsblatt newspaper. Translation contributed by Jennifer Stahl.