With most clubs eager to sell stadiums or their rights to major sponsors for cash, Union, once East Germany's anti-regime team with a strong working-class culture, are choosing to offer them to their own fans.
There are 10,000 shares at 500 euros each on offer with the expected five million euro in revenue going towards paying off debt and helping rebuild the main stand.
"Hundreds of people have been lining up since early in the morning and the fax machine with which people also can apply to buy shares has not stopped ringing all day," a club official told Reuters.
"We have nine people processing applications non-stop as we speak."
It is not the first time Union, bitter rivals of secret police Stasi-supported Dynamo Berlin in the old East Germany, have called on their fans for support, with hundreds volunteering to help rebuild the stadium in 2009.
The club also organised a blood donation event and cancelled a multi-million sponsor's contract after one of the company's directors was exposed as a former Stasi officer.
"Union is selling its soul," club boss Dirk Zingler said last month when the initiative was unveiled. "To the fans."
"We want to show that we have found our own way of doing things."
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