But by February of this year, the government said it wanted to review the deal by CCCI, the overseas arm of CCCC, under the Canada’s National Security Review of Investments Act. In Canada, any deal involving a state-owned company worth more than 398 million Canadian dollars, or about $310 million, can be subject to a review if the government believes it could be “injurious to national security.”

On Wednesday, the government said it blocked the deal that based on its findings “in order to protect national security,” without elaborating.

“Our government is open to international investment that creates jobs and increases prosperity, but not at the expense of national security,” Mr. Bains said.

The Canadian government did not give details about its decision, but one of the biggest hurdles facing the deal, according to analysts, was Aecon’s contract for Canada’s Candu nuclear reactors, which generate electric power.

Earlier this year, Canada’s Conservative Party called for a review of the deal and raised concerns about Aecon’s contracts with both the military and the nuclear industry. Members of Parliament also cited bribery allegations against one of CCCC’s units in Bangladesh. In January, the finance minister of Bangladesh said it was blacklisting China Harbour Engineering Company, a subsidiary of CCCC, after allegations arose that it tried to bribe an official.

“For reasons that have more to do with political opinion and the desire to limit competition, some opponents of the deal have made completely false claims about the nature of Aecon’s business and what may happen if it joins CCCI,” John M. Beck, president and chief executive of Aecon, and Lu Jianzhong, president of CCCC, wrote in an op-ed article in The Globe and Mail, a Canadian newspaper.

CCCC is controlled by the Chinese state, but it is publicly listed and has shareholders that include the Canada Pension Plan Investment Board, BlackRock and Vanguard, Mr. Beck and Mr. Lu wrote.