Account holders at Deutsche Bank, Commerzbank, Dresdner Bank and Targobank are most likely to experience delays, daily Financial Times Deutschland reported. These banks have only sent a portion of their customers’ files for 2009 related to the government’s 25 percent tax on investment income such as interest payments and dividends.

This could mean that many won’t be able to file their tax forms by the May 31 deadline, the paper said.

The banks have reportedly been trying to adjust their systems for months to suit complex new rules first released by the Finance Ministry on December 22 in a 150-page document.

Some 719,000 private customers at Commerzbank subsidiary Comdirect are said to be still awaiting their account balances, while another 300,000 at Targobank are still empty-handed. Many of these customers are owners of foreign investments, though normal citizens and pensioners will also face delays, the paper said.

The original version of this article mistakenly mentioned capital gains when meaning unearned income such as interest and dividends. We have corrected the error.