Prosecutors have been using previously empaneled grand juries to issue subpoenas and gather evidence in an investigation that has spanned the better part of two years.
Grand juries only sit for a few months at a time. A special grand jury sits for a longer period of time.
Empaneling a special grand jury suggests the case has reached an advanced stage, but as yet, there have been no charges filed.
Potential witnesses have been contacted in recent weeks about appearing before the special grand jury, the sources told ABC News.
Word of the special grand jury's existence was first reported by the Washington Post.
Manhattan DA Cy Vance began investigating Trump's business practices based on the Congressional testimony of Michael Cohen, who served as the former president's personal attorney and fixer.
One focus of the investigation includes whether Trump inflated the value of certain properties to obtain bank loans and deflated the value of those same properties to pay lower taxes.
Vance fought all the way to the U.S. Supreme Court twice to gain access to eight years' worth of Trump's personal and business tax returns.
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