June 13 (Reuters) - William Ackman's Pershing Square Capital Management said it had filed a lawsuit seeking confirmation that a requested special shareholder meeting of Allergan Inc's shareholders would not trigger Allergan's poison pill takeover defence.
The Botox maker has rejected a $53 billion joint offer from Ackman and Canadian drugmaker Valeant Pharmaceuticals International .
Allergan said in April that its board had adopted a one-year shareholder rights plan to give it more time to consider takeover proposals.
Allergan's shareholder rights plan will trigger if a person or group acquires 10 percent or more of its shares.
The lawsuit filed in Delaware Court of Chancery followed a request to Allergan from Pershing Square on June 6 seeking confirmation that Allergan would not use its poison pill to impede Ackman's request for a special meeting.
A response from Allergan's counsel on Thursday did not provide that confirmation, Pershing Square said.
Allergan rejected a sweetened offer from Valeant and the activist investor on Tuesday.
(Reporting by Natalie Grover and Sweta Singh; Editing by Ted Kerr)