Perrigo Co Plc rejected Mylan NV's unsolicited $27 billion tender offer, saying it substantially undervalued the company and did not adequately compensate shareholders.
Dublin-based Perrigo said shareholders should "just say no" by taking no action.
Netherlands-based Mylan launched its tender offer on Monday.
Morgan Stanley is Perrigo's financial adviser. (Reporting by Amrutha Penumudi in Bengaluru; Editing by Ted Kerr)