Pfizer (PFE) said late Friday it filed a lawsuit against Metsera (MTSR), its board of directors, and Novo Nordisk (NVO), for allegedly breaching terms of its merger agreement with Metsera.

Pfizer said the lawsuit seeks to block Metsera from terminating the merger agreement and proceeding with an alternative proposal from Novo Nordisk, which Pfizer claims cannot qualify as a "superior company proposal" under the deal terms due to significant regulatory risks.

Pfizer said the US Federal Trade Commission already granted early termination of the waiting period under the Hart-Scott-Rodino Act for its pending Metsera acquisition and the transaction is "ready to complete" following Metsera's stockholder meeting on Nov. 13.

Pfizer alleged that Novo Nordisk's proposal is "an illegal attempt by a company with a dominant market position to suppress competition" and uses an unprecedented structure to evade antitrust review.

Metsera said in a separate press release it "disagrees with the allegations in Pfizer's complaint and will address them in the Delaware Court of Chancery."

Metsera and Novo Nordisk did not immediately respond to MT Newswires' request for comment.