Bill Ackman's Pershing Square hedge fund increased its stake in Canadian Pacific Railway during the third quarter, according to a securities filing released Monday .
Pershing Square held just under three million shares at the end June.
Ackman previously served as a board member at Canadian Pacific, pushing for a takeover of Norfolk Southern that never happened.
It is not clear how many, if any, additional shares Ackman bought outside of those forward contracts.
Ackman is an activist investor, known for pushing for change in a small group of portfolio companies.