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Lighthizer will testify before the Appropriations subcommittee responsible for the Commerce Department.

Earlier on Friday, Trump said he was "ready to go" if he needed to impose tariffs on all $500 billion-worth of Chinese imports to the U.S.

Trump has already imposed tariffs on $34 billion of Chinese imports, plus tariffs on steel and aluminum, solar panels and dishwashers. Another $16 billion in tariffs are in the works for China, and Trump has directed his administration to look into further penalties on foreign cars.

China has retaliated with its own tariffs against U.S. exports, as have major trade partners affected by the tariffs, including Canada, Mexico and the E.U.