Hogan & Hartson partners have voted in favour of creating a new Berlin office with a group of senior Oppenhoff & Rädler lawyers.
The move follows discontent among some of the Oppenhoff partners in Berlin because Linklaters & Alliance, which the firm has recently merged with, was mainly interested in the Frankfurt office.
The US firm is due to gain 12 partners and the number could rise. The Lawyer revealed last week that a group of Oppenhoff partners were in talks with Hogan & Hartson.
The new firm will be called Hogan Hartson & Raue and is expected to be operational within the next three months.
Following the vote in favour of a merger with Linklaters, 23 of Oppenhoff's 116 partners expressed their desire to leave. It is thought the figure could rise to as many as 42, which would leave a significant gap in the German partnership.
Berlin senior partner Peter Raue and top media and telecoms lawyer Christoph Wagner are among the group of 30 going to Hogan & Hartson.
Wagner refuses to be drawn on specifics but he does confirm he is in discussions with other Oppenhoff partners about joining the firm.
Oppenhoff declines to comment but it is understood that all partners have until September to decide their future as that is when the two firms to sign the merger documents.
Wagner says the decision to hook up with the US firm was prompted by Linklaters' lack of interest in Berlin. He says: "Linklaters has a focus on Frankfurt, Frankfurt and again Frankfurt and we are in Berlin.
"We want to be in the focus of our firm. If it has a focus on Frankfurt, then Frankfurt will grow and we will not be able to hire the brightest associates for Berlin."
Wagner adds that the BSkyB alliance with German TV group Kirch, on which Oppenhoff and Hogan & Hartson acted for the media giant, was one of the largest in the firm's history, yet was done out of the Berlin office.
His relationship with long-standing client BSkyB is also one of the reasons for his departure as a conflict of interest may arise.
Hogan & Hartson managing partner Bob Odle says the decision to open in Berlin started with Wagner. He says: "It all got going through [Wagner] who has been a close friend and professional colleague to many of us here for many years."
But he adds that the German capital is an attractive market because of its similarities with the Washington market, where the firm is based.
The aim is to create a full service office, specialising in a range of work including regulation, corporate, M&A, media and litigation. It will then focus on opening more German offices, possibly in Frankfurt and Munich.