All three major US indices finished lower, ending six straight days of records for the S&P 500 and Nasdaq.
Shares of several US-listed companies that have benefited from NAFTA fell sharply on news Canadian officials increasingly view President Donald Trump as likely to abandon the trade pact. These included General Motors, beer and spirits marketer Constellation Brands and railroads Kansas City Southern and Canadian Pacific Railway.
Unease over NAFTA also sent the Mexican peso and Canadian dollar sharply lower against the US currency.
Earlier, equity markets in Paris and Frankfurt retreated as the euro advanced against the dollar following a Bloomberg News report that officials reviewing China's foreign-exchange holdings have recommended slowing or halting purchases of US Treasuries.
"The euro initially gained on speculation that any reduction in US bond purchases by China could result in increases to its holdings of euro zone assets," said Omer Esiner, analyst at Commonwealth Foreign Exchange.
The euro got as high as $1.2020 before pulling back somewhat.
Oil prices continued to push higher, boosted by a US inventory report that showed stockpiles of crude fell 4.9 million barrels last week.
Crude prices have more than doubled from lows below $30 in early 2016, supported by an output freeze deal between OPEC and Russia and, recently, tensions in the oil-rich Middle East.
Market-watchers say unrest in key producer Iran could dent the country's capacity, while others point out that any suppression of protests by Tehran could lead Trump to reimpose export sanctions.