A company that's taking on a bigger role in Air Products has revealed itself.

Pershing Square Capital Management says it's the largest Air Products stakeholder.

The group run by hedge fund manager William Ackman owns $2.2 billion in stock -- just under 10-percent of the company.

Last week Air Products adopted a so-called "poison pill" plan that kicks in at 10-percent -- to block a potential takeover.

Air Products says Pershing Square has not contacted them but they say they welcome new investors and look forward to engaging with Pershing Square.