President Donald Trump once again ratcheted up the tension in his ongoing trade dispute with China on Thursday, threatening to slap tariffs on an additional $100 billion in imports from one of the United States largest trading partners.

These tariffs would come on top of separate duties on $50 billion in U.S. imports of Chinese products like motor vehicles and home appliances that the administration announced earlier this week.

China had responded to that announcement by releasing its own list of products worth roughly the same amount that it will target with duties if the Trump administration moves forward with the presidents course of action. That list of more than 100 items was heavy on agricultural commodities, especially soybeans. Beijing also said it would add 25 percent tariffs on U.S. exports like aircraft, automobiles and chemicals.

Trump said in a statement Thursday evening that he found Chinas retaliation “unfair,” and, for that reason, he instructed U.S. Trade Representative Robert Lighthizer “to consider whether $100 billion of additional tariffs would be appropriate … and, if so, to identify the products upon which to impose such tariffs.”

“Rather than remedy its misconduct, China has chosen to harm our farmers and manufacturers,” Trump said. “I am committed to enabling American companies and workers to compete on a level playing field around the world, and I will never allow unfair trade practices to undermine American interests.”

U.S. markets reacted negatively on the news with the Dow Jones Industrial Average showing an implied open down more than 400 points.

The administration is moving to impose tariffs as one step in a multipart effort to counter Chinese policies that the White House argues force U.S. technology companies to surrender billions of dollars in intellectual property and other proprietary information to gain access to Chinas state-controlled economy.

Trump also announced Thursday that he will instruct Agriculture Secretary Sonny Perdue “to use his broad authority to implement a plan to protect our farmers and agricultural interests.”

Lighthizer praised Trumps decision to consider another $100 billion worth of products to target with a 25 percent tariff as “appropriate.”

He said Beijing should have reacted by changing its own policies, but “unfortunately, China has chosen to respond thus far with threats to impose unjustified tariffs on billions of dollars in U.S. exports.”

“Such measures would undoubtedly cause further harm to American workers, farmers and businesses,” he said. “Under these circumstances, the president is right to ask for additional appropriate action to obtain the elimination of the unfair acts, policies and practices identified in USTRs report.”

It is unclear how the U.S. Department of Agriculture will alleviate the pressure on American farmers. Perdue acknowledged the request and stated, “As we take a stronger approach to the way we handle trade as a nation, we will use all of our authorities to ensure that we protect and preserve our agricultural interests.”

On Wednesday, Perdue said the prospect of a prolonged trade war could require that Capitol Hill lawmakers take “some extraordinary measures” in the next farm bill.

Despite such reassurances, many farmers have expressed anxiety about the escalating trade war. Trump administration officials have played down the harm to the American economy from Chinese retaliatory measures, but farmers of commodities and other products have already been under stress from falling prices and Trumps war of words on trade including a pullout from the TPP.

Congressional leaders representing farm states have also been worried about the tit-for-tat promises of retaliation. On Thursday, Senator Ben Sasse of Nebraska accused Trump of not have a realistic plan for reining in Chinas trade problems.

Trump is “threatening to light American agriculture on fire. Lets absolutely take on Chinese bad behavior, but with a plan that punishes them instead of us,” Sasse said. “This is the dumbest possible way to do this.”

None of the U.S. tariffs aimed at getting China to change its intellectual property practices have taken effect. The Trump administration has laid out a consultative process that will prevent duties on the initial $50 billion worth of products from being formally implemented until late May, at the earliest. Beijing has also indicated that the implementation date for its retaliation will depend on when the U.S. government moves forward.

Potential tariffs on the additional $100 billion in imports from China that could be targeted will also be subject to a similar public comment process, Lighthizer said Thursday.

The administration previously imposed tariffs on steel and aluminum imports from a broad range of countries, including China. Beijing also announced this week that it would be retaliating against those duties with penalties on 128 U.S. products worth roughly $3 billion.

Catherine Boudreau and Adam Behsudi contributed to this report.