FRANKFURT (Reuters) - New details emerged on Wednesday of a deepening boardroom tussle at a leading online broker in Germany, with a document claiming that a significant contingent of investors had demanded a change of chief executive in November but was stalled by the chair.

Investors representing 35% of shares at the online broker, FlatexDegiro, wrote to the company's supervisory board in November asking it to replace the CEO, Frank Niehage.

But the request was initially ignored by the board's chair and only taken up after repeated entreaties, the document seen by Reuters said.

Niehage suddenly resigned last month but now the focus is on Chair Martin Korbmacher.

The recounting of events was described in a document for the broker's annual general shareholder meeting next month. The version of events is presented as justification for ousting Korbmacher at that meeting.

FlatexDegiro declined immediate comment.

Korbmacher did not immediately respond to a request for comment. He has previously declined to comment or not responded to requests.

The broker's top investor and company founder Bernd Foertsch has been behind the push to oust the chair, telling Reuters earlier this week that he wanted a "fresh start" for the company.

A spokesperson for Foertsch confirmed the accuracy of the document but asked Reuters to make clear the spokesperson was not the source.

The dispute is part of an ongoing, escalating and unusually public boardroom strife in Germany, where power struggles are usually behind closed doors.

(Reporting by Tom Sims; Editing by Miranda Murray and Emelia Sithole-Matarise)

By Tom Sims