Exiting Nafta would be a major break from decades of US trade policy, and it's unclear whether the order would be a serious threat to leave the pact or simply an effort to put the country's neighbours on notice that Trump intends to rewrite the rules of North American trade.
Even threatening to withdraw from Nafta could heighten tensions with Mexico and Canada, close allies and trading partners.
Trump railed against Mexico repeatedly during his campaign, saying that its trade practices are ripping off US workers and luring away US jobs - adding to tensions over Trump's proposed border wall and his remarks about Mexican immigrants.
In recent days, however, he has taken a harder line with Canada, blasting a recent change in the dairy pricing policy there. And on Tuesday, the Commerce Department said it would begin charging a tariff on the import of softwood lumber from Canada into the United States, alleging Canada was improperly subsidizing its domestic timber firms.