Renegotiating the North American Free Trade Agreement could take until next year, US Commerce Secretary Wilbur Ross said Monday.
The remarks underscore the pressures facing the current administration as it attempts to deliver on one of President Donald Trump's signature campaign pledges.
Speaking at a trade event near Washington, Ross said that in an "ideal world" talks would be completed in 2017 but that would mean talks would have to happen at "record speed."
"So, I don't know whether we'll be able to do that," he said. "But we're certainly mindful of the calendar and the fact that the calendar is fundamentally not our friend."
The Trump administration last month gave lawmakers 90 days' notice of the administration's intention to start to renegotiate the 1994 trilateral trade pact with Mexico and Canada, and talks are due to begin in August.
But the talks could be complicated by Mexico's general elections in July 2018, which observers say mean President Enrique Pena Nieto may not have a free hand for bargaining; and by campaigning for the US congressional midterm elections late next year.
In addition, there is the expiration in mid-2018 of "fast-track" authority which provides streamlined treatment in the US Congress of any trade legislation, although Congress could extend the rule for another three years.
On the campaign trail, Trump described NAFTA as a "disaster" for the United States and vowed to exit from the deal. But he retreated from those threats once in office following pleas from Mexican and Canadian officials.
The Trump administration has taken an aggressive stance on trade issues, and waded into several disputes with Canada, over lumber and dairy, and with Mexico over sugar.
Trump also pledged to be tougher on unfair trade practices with countries like China, and on Monday, the Commerce Department announced yet another trade complaint against that country, this time over plywood.
Commerce said preliminary results found Chinese exporters were selling hardwood plywood on the US market at prices that are as much as 114.7 percent below fair value.
A final determination in the anti-dumping complaint brought by several American lumber companies is due in August, but US customs will begin to collect duties immediately, the Commerce Department said.
Last year, the trade in plywood, widely used in construction, was valued at $1.1 billion.
In April, Trump invoked national security interests in ordering a probe of steel imports from China, which many trade experts say is flooding the world market and driving down prices.