Bill Ackman’s Pershing Square Capital Management said Tuesday it increased its stake in Canadian Pacific Railway (CP, CP.T) to 14.2% from 12.4% after buying three million shares this month. In the regulatory filing, Pershing, led by value investor Bill Ackman, didn’t update the progress of its discussions with the railroad’s management.

On Dec. 1, Pershing said it was seeking unspecified changes to Canadian Pacific’s business.