A whopping 74% increase in tariffs since last year added $6 billion in extra costs for U.S. consumers and businesses, a pro-trade group said.

The group also warned additional tariffs threatened by President Donald Trump would further hit demand and hurt jobs.

The U.S.-China trade war has intensified this week after Washington branded Beijing a currency manipulator and said it would impose 10% tariffs on the remaining $300 billion in Chinese imports, starting on Sept. 1.

Trump on Wednesday repeated his tough stance on China, saying his actions would ultimately benefit the American economy.

The trade group, called Tariffs Hurt the Heartland, which includes the Americans for Free Trade coalition and Farmers for Free Trade, disagreed with Trump's position. It said the 74% rise from the same period a year ago was one of the highest monthly jumps on record.

"We are at a very dangerous pivot point with the tariff strategy," David French, senior vice president of government relations at the National Retail Federation, a coalition member, said in a conference call with business leaders on Wednesday.

The trade coalition said American taxpayers have paid over $27 billion in extra import tariffs from the beginning of the trade war in 2018 through June of this year based on data collated from the U.S. Census Bureau and the U.S. Department of Agriculture.

Jo-Ann Stores, an Ohio-based arts and craft retailer, hit by tariffs introduced in September 2018, said it has already been forced to raise prices, and has seen that decrease demand.

"It's an enormous financial burden," said Jo-Ann Chief Executive Officer Wade Miquelon, who previously served as chief financial officer of Walgreens. "These tariffs will cut into our profit margins and force us to take very tough decisions including job eliminations and further store closings."

Florida-based toy maker Basic Fun! expressed worry about lower demand in the months leading up to Christmas.

"All the volatility that this talk of tariffs and everything else is making the consumer spend less," Jay Foreman, the company's chief executive, said. "We are seeing and hearing that the consumer is not coming out as strongly already."

Other business leaders on the call said tariffs will increasingly threaten U.S. jobs by not only injecting demand volatility but also through upending supply chains.

"As prices go up and demand decreases it is a fact: American jobs will be lost," said Lance Ruttenberg, chief executive of American Textile Company.

In addition to the tariffs introduced last year and early this year, the Trump administration's latest list of tariffs cover virtually every consumer import from China.