The decision by the commission deals a blow to the North Pacific Paper Company, which filed a complaint last year arguing that dumped and subsidized imports of uncoated groundwood paper from Canada were depressing prices and eroding profitability.

Norpac was the only manufacturer to file a complaint. The rest of the industry has blamed the declining print newspaper business, rather than Canada, for its struggles. The situation thrust Norpac and its owner, the private equity firm One Rock Capital Partners, into the spotlight as newspapers complained that their costs were surging as a result of the tariffs.

One Rock, which is based in New York, bought the mill in 2016 and, according to people within the paper industry, most likely paid a premium for the business in hopes that it could make the case for tariffs and boost the business’s revenue. Now it appears that bet has been lost.

“We are very disappointed in the U.S.I.T.C.’s negative determination, given that the record clearly shows that the domestic industry has been materially injured by dumped and subsidized imports from Canada,” said Craig Anneberg, Norpac’s chief executive. “We intend to review the U.S.I.T.C.’s written determination when it is issued in a few weeks, and we will assess our options at that time.”

The ruling was welcomed by the Canadian manufacturer Catalyst Paper Corporation, which had been exporting more than 425,000 metric tons of newsprint into the United States before it was singled out and hit with the heaviest levies.

“Our industry continues to face a challenging operating environment stemming from increasing costs and declining demand,” Ned Dwyer, the president of Catalyst, said in a statement. “Today’s ruling is a welcome break for Catalyst, our customers, employees and the communities where we operate.”

While the tariff ruling offers a reprieve to newspapers, publishers say it may not result in jobs coming back or pages being restored. Instead, it probably just accelerated cost-cutting that would have eventually occurred anyway, given the industry’s declining readership and revenue.