A new report says potential changes to NAFTA and a loss of free trade with the United States represent the biggest concerns for a number of big American firms operating in this country.

The American Chamber of Commerce in Canada says 38 per cent of the companies participating in its study said they believed that free trade was the biggest concern for their business.

Other concerns included President Donald Trump (19 per cent) and Buy American policies (11 per cent).

The report's release on Monday coincides with the third round of talks between Canada, the United States and Mexico — which are working to renegotiate the North American Free Trade Agreement.

An agenda for the current round of negotiations, the first held in Ottawa, showed the environment, rules of origin for automotive content, agriculture and labour standards were to be addressed during this week's talks.

However, the AmCham report is based on findings of a Nanos Research survey conducted between March 15 and July 19, prior to the first round of talks that were conducted in Washington from Aug. 16 to 20.