US firm Hogan & Hartson is in merger talks with New York litigation practice Davis Weber & Edwards.
The deal would boost Washington DC-based Hogans' Manhattan presence from nine lawyers to more than 50.
Hogan & Hartson, which has an office in London, has opened six new offices in the last five years. Bob Glen Odle, Hogans' managing partner, says only that the firm is "in discussions with a New York firm". Davis Weber refuses to comment.
Davis Weber was set up in 1980 by six former associates from top Wall Street firm Cravath Swaine & Moore.
It is highly rated in securities, antitrust and professional responsibility. The firm planned to open offices around the US in the early 1990s but has since lost a number of partners. It has a blue-chip client base, which includes IBM and AT&T.