A British firm extended its merger offer to JWT.

WPP Group extended a $50.50 a share bid for the parent of J. Walter Thompson advertising agency until June 22 while negotiations continue. Separately, JWT disclosed that a shareholder has filed a class-action suit against it in Delaware Chancery Court. The suit alleges that several JWT directors did not act in the shareholders’ interests when they stated that JWT, its ad agency and its Hill & Knowlton unit were not for sale. The suit asks the court to order JWT’s directors to put the firm up for sale and “take whatever action is necessary to enhance shareholder value.”