"We have had no notification from Bafin yet. We therefore have no comment," a Dresdner Bank spokeswoman told AFP.
But a BaFin spokeswoman confirmed it had received the letter: "We will examine it now, of course."
In the letter, of copy of which was obtained by AFP, the second-biggest German airline said Dresdner Bank published an analyst's research note on July 17 predicting that Air Berlin shares could fall to zero and that the airline was threatened by bankruptcy.
On Friday, shares in the airline were being traded for about €3.40. "Shortly before and after this release, Dresdner Bank made many transactions with Air Berlin shares" at a level that was "far above those that it normally makes with the stock," the letter alleged.
That raised the prospect of short-selling, a process by which investors try to make money by speculating that the price of a share will fall in the near term, Air Berlin added.
In addition, it said that the note by Dresdner Bank analysts was "false and unbalanced in many aspects." It asked stock market authorities to check whether Dresdner Bank had committed insider trading, share manipulation or breaches of its responsibility to objective financial analysis.
A spokesman for Air Berlin also told AFP that it "was considering the possibility of launching civil proceedings."
The airline is now paying the cost of an explosive growth strategy that was marked by the purchase of several competitors and major orders for new aircraft.
A sharp increase in the price of jet fuel has forced Air Berlin to trim its fleet by 10 percent and to lower its 2008 earnings outlook twice. The airline has also given up on a goal of establishing regular flights to China and of buying Condor, an airline owned by the Thomas Cook travel group.