Led by the company's largest shareholder, Bill Ackman, investors owning 31% of Botox manufacturer Allergan have called for a special shareholder meeting.

Ackman's investment vehicle, Pershing Square Capital Management, said it filed a lawsuit in the state of Delaware to require Allergan to schedule the meeting.

At the meeting, the activist shareholder hopes to replace the bulk of Allergan board members with his own slate of directors who might agree to the takeover deal and to force the pursued company to open discussions.

Pershing Square and Valeant Pharmaceutical International made a $52 billion hostile offer for Allergan in April. Since then Allergan has been fighting for investor support for its own stand-alone plan that includes cost cuts and making an acquisition of its own.

Meanwhile, Ackman, who has been working to sign up enough shareholders, said that under its bylaws Allergan is required now to call the meeting no later than Dec. 20.

Ackman and Valeant's cash and stock offer is now worth $49 billion, which Allergan said is not enough

The lawsuit is the latest legal tussle for the companies and follows Allergan's insider trading suit against Valeant and Ackman filed in a California federal court on Aug. 1.

Allergan said in a statement it would review the requests from shareholders in connection with Pershing Square's meeting request and report the results promptly after its review.