NEW YORK (Reuters) - (This Dec. 9 story has been corrected to attribute quotes to Ben Hackett of Hackett Associates consulting firm, not Jonathan Gold, vice president for supply chain and customs policy at the NRF, in paragraphs 3 and 8) The United States' busy ports kicked activity up a notch in November and December, when inbound cargo traffic is set to reach new records, the National Retail Federation industry group said on Monday. 

Retailers had already been front-loading purchases due to a shortened holiday season and shipping bottlenecks worldwide, but the prospect of a mid-January port strike and tariff increases planned by President-elect Donald Trump has big importers accelerating their buys.

"The window to front-load goods on vessels arriving before a potential strike is quickly closing. Then there are issues as President-elect Trump promises to increase tariffs," said Ben Hackett, founder of Hackett Associates, a consulting firm.

The International Longshoremen's Association union and the United States Maritime Alliance (USMX) employer group were at odds as of November, after temporarily suspending a strike in October. A strike could strangle activity at ports stretching from Maine to Texas once the contract ends on Jan. 15.

October's three-day strike was the first large-scale strike at East Coast and Gulf Coast ports in nearly 50 years, which caused a summer rush of imports to the United States.

Trump's proposals for tariffs of 10% to 20% on all imports and a 60% or more tariff on goods from China have added to retailers' anxiety. Between September and mid-November, more than 200 companies in the S&P 1500 Index mentioned tariffs on conference calls or at investor events as an issue.

Trump promised an additional 25% tariff on goods from Canada and Mexico and a further 10% tariff on China unless the three countries clamped down on illegal immigration and fentanyl flowing into the United States.    

"Shippers are moving up as much cargo as they can before then," Hackett added. 

NRF, which counts the country's largest shippers, Walmart, Target and Lowe's among its members, said in a Monday report it expects November container volumes to hit a record 2.17 million 20-foot equivalent units (TEUs), up 14.4% from a year earlier. December volumes are forecast at a record 2.14 million TEUs, up 14% year over year, NRF said.

U.S. shoppers could lose up to $78 billion in annual spending power annually if Trump's tariffs proposal on all imports are implemented, a previous NRF study showed.