Pfizer is suing over some unsolicited competition in its nearly $5 billion bid to buy the drugmaker Metsera.

New York-based Pfizer said Friday after markets closed that it was suing Metsera and a third drugmaker, Denmark’s Novo Nordisk, over a bid for Metsera that Novo announced Thursday.

Novo said it planned to buy Metsera in a deal that could be worth up to $9 billion, and Metsera said the offer appeared to be superior to Pfizer’s bid, which was announced in September.