NEW YORK (Reuters) - The unloading of hundreds of containers with imported coffee beans at the United States' East Coast ports has stopped due to the strike of portworkers, aggravating the tight supply in the largest coffee-drinking nation.

The delays in delivery of imported coffee to U.S. roasters and coffee chains could further increase bean prices which hit multi-year highs last week due to limited supply, and raise costs for companies and consumers.

Prices for coffee held in U.S. warehouses are already rising due to the delays, said one coffee trader with containers stuck in ports.

"We have some 40 containers waiting to be moved," said the head trader of one of the largest coffee importers in the U.S., which supplies roasters and cafeterias nationwide.

"The owners of the containers already told us they will charge additional fees if the boxes take longer than normal to be returned," he added, asking not to be named because he was not authorized to speak publicly on the issue.

A portworkers strike entered its second day on Wednesday, halting the movement of containers through ports from Maine to Texas, affecting shipments of hundreds of products including food.

Some coffee sellers have stopped offering spot deals as they wait to see how the strike develops, said a second trader.

U.S. coffee stocks are at a low historical level, the traders said, since importers have been avoiding high inventories to reduce storage costs during a period of high interest rates. That situation makes the port problems worse.

"Some regions (in the U.S.) might have a supply squeeze," said the first trader.

Industry participants believe, however, that the labor issue could be quickly solved because the magnitude of the problem demands attention.

"We source coffee from 35 different countries. If this (strike) goes on for a long time, everybody will be impacted," said Will Ford, president of operations at Arkansas-based Westrock Coffee Company.