Based on available industry data, tires imported from China represented nearly 50 percent of overall aftermarket truck and bus tire shipments in 2015.
Truck and bus tire imports from other countries also grew during the period, the USW said, but are much less significant combined than Chinese imports.
Testimony at the hearing included statements from USW union local presidents who said that production fell sharply at their facilities between 2013 and 2015 because of unfair competition from Chinese imports.
"When we asked management why they were cutting production, they told us that Chinese tires were killing the market and that sales simply weren't there for the company," said Billy Wright, president of USW Local 1155 organizing workers at the Bridgestone Americas plant in Warren County, Tenn.
Members of Congress also testified on behalf of the USW at the hearing.
Sen. Tim Kaine, D-Va., testified on behalf of the Goodyear plant in Danville, Va., which he said employs more than 2,000 including more than 1,800 USW members.
"These production declines directly impact American workers, who suffer lower overtime and take-home pay, and ultimately, if unfair trade is not stopped, layoffs," Mr. Kaine said.
The two sides at the hearing disagreed at the most basic levels. Whereas the USW printed in its testimony an advertisement for Double Coin tires listing domestic brands as direct competitors, representatives of the Chinese industry said they competed largely with each other, third-country tire importers and retreaders.
U.S. tire manufacturers are operating at full capacity, and imports are necessary to meet demand, spokesmen for the Chinese industry said.
"U.S. truck and bus tire producers do not have sufficient capacity to supply the U.S. market," said Gary Schroeder, director, global truck and bus tires at Cooper Tire & Rubber Co., which sources all of its Roadmaster-brand truck and bus tires from China.
Even the new commercial tire plant in Mississippi opened in 2015 by Yokohama Tire Corp. and one under construction by Continental A.G. in the same state will not end the need for Chinese tire imports, he said.
A major subtopic at the hearing was whether 10x20 bias tube-type tires from China, used exclusively for marine intermodal chassis fleets, compete with domestic truck tires, as the ITC ruled in its preliminary determination.
Advocates for the USW said the bias tires were easily interchangeable with domestic radial truck tires. However, representatives of the marine intermodal chassis industry disagreed.
"To the best of my knowledge, we're are the only industry currently using 10x20 bias-tube tires in the United States," said Bernard Vaughan, chief legal officer and executive vice president of Kenilworth, N.J.-based Flexi-Van Leasing Inc. "There has not been any production of 10x20 bias tube tires in the United States since the early 1990s."
The bias tube tires require two-piece rims, Mr. Vaughan said. If intermodal fleets were forced to switch to radial or tubeless tires, the switch to one-piece rims alone would cost the industry more than $1 billion, he said.
The ITC is scheduled to make its final vote in the investigation March 6. If it votes in the affirmative, final antidumping and countervailing duty orders would be issued March 13.
According to Commerce figures, the volume of Chinese truck and bus tires imported into the U.S. rose to 8.9 million in 2015 from 8.4 million in 2014 and 6.3 million in 2013.