Stung by the mass defection of all of its partners in London and Moscow, New York-based Coudert Brothers is exploring a possible lawsuit against San Francisco’s Orrick, Herrington & Sutcliffe, the firm that hired the partners away.

Stung by the mass defection of all of its partners in London and Moscow, New York-based Coudert Brothers is exploring a possible lawsuit against San Francisco’s Orrick, Herrington & Sutcliffe, the firm that hired the partners away.

Coudert Brothers has retained Barry Ostrager, the co-head of the litigation department of Simpson Thacher & Bartlett, to conduct an investigation into whether Orrick and the departing partners breached confidences gained in merger discussions between the two law firms.

Orrick announced last week that it had hired 11 partners from Coudert: eight in London and three in Moscow. The move left those offices, previously among Coudert’s strongest, with only associates and other junior lawyers.

In a letter to Orrick Chairman Ralph Baxter dated Monday, Ostrager refers to merger talks between 700-lawyer Orrick and 600-lawyer Coudert that took place before the London and Moscow partners’ departures.

“We have reason to believe that during the period these discussions were occurring Orrick and the departing Coudert partners may have engaged in breaches of fiduciary obligations and/or tortious conduct,” Ostrager wrote.

The letter states that the investigation will focus on e-mail and other communications between Orrick and the departing partners.