One of the largest shareholders in Canadian National Railway Co. said it’s prepared to launch a proxy fight to replace the company’s leader as the $30 billion deal to buy Kansas City Southern faces possible collapse.

Canadian National Railway Co.’s $30 billion takeover bid for Kansas City Southern received a boost Aug. 6 when a prominent shareholder advisory firm recommended that shareholders support the deal.

ValueAct Capital Management has built a new position in Nikola Motor Co., a closely held hydrogen fuel cell trucking company seeking to raise $1.5 billion to expand in the U.S., starting on the West Coast.

Hunter Harrison, Canadian Pacific Railway’s chief executive officer, said his greatest fear in moving crude by rail is the prospect of a terrorist attack on the company’s trains.