OTTAWA — Resource companies and manufacturers in Canada faced disruptions after a strike shut down the Canadian Pacific Railway early Wednesday morning.


The strike by about 4,800 locomotive engineers, yard workers, conductors and rail traffic controllers came just days after Fred Green stepped down as the railroad’s chief executive and William A. Ackman, the activist American investor, won a proxy battle for control of the company. Canadian Pacific has about 15,000 miles of track in North America and controls an effective duopoly over rail traffic in Canada with the Canadian National Railway. The mining, forestry, agriculture and energy companies which form much of the Canadian economy depend heavily on rail shipments. And key manufacturing industries, particularly automakers, also rely on trains.


Because of Canadian Pacific’s economic importance, Lisa Raitt, the federal labor minister, met with officials from the railway as well as the Teamsters Canada Rail Conference in Ottawa on Tuesday.


Ms. Raitt ended walkouts at Air Canada through legislation and there was speculation in Canada on Tuesday that the Conservative federal government may intervene in the Canadian Pacific shutdown after citing its negative economic impact. While the Air Canada legislation was condemned widely by unions, it appeared to be popular with travelers.


It was not clear early Wednesday what forced the strike. The Teamsters only announced the walkout through a post on Twitter and indicated that negotiations would resume later in the day. In a statement issued on Saturday, the union said the main stumbling blocks were “work rules, fatigue management, and the pension plan, which the employer wants to cut by 40 percent.”


Canadian Pacific had no immediate comment. But on Saturday it said that its employees pension benefits must become “industry-comparable.”


At Ms. Raitt’s request, Canadian Pacific agreed on Tuesday to an offer from the union to continue operations of commuter services which use the company’s tracks and crews in Toronto, Montreal and Vancouver, British Columbia.


The strike, however, will shut down a small number of intercity routes. Via Rail Canada, the government owned passenger rail system, said in a statement on Tuesday evening that trains between Ottawa and Toronto may be canceled as well as service on a remote line in northern Ontario.


Rocky Mountaineer Rail Tours said late Tuesday that some of its of its luxury trips in western Canada along Canadian Pacific lines would be disrupted.


While Canadian Pacific’s new board is just beginning the hunt for a new chief executive, Mr. Ackman has been promoting E. Hunter Harrison, the former chief executive of Canadian National, as his ideal leader. While Canadian National has a long history of poor relations between management and unions, union leaders argue that it deteriorated during Mr. Harrison’s tenure.