President Trump directed top trade officials to study retaliatory tariffs on global trading partners that have steep import duties on U.S. goods, a process that could take several weeks to complete. Why it matters: It threatens a historic attack on global trade norms to address what Trump has deemed unfair imbalances,

President’s memo asks agencies for more details on how to adjust U.S. tariffs to reflect the duties imposed by other nations.

Reciprocal tariffs refer to tariffs—the taxes charged on imported goods—the U.S. government plans to levy against global trading partners that are equal to the existing tariffs foreign countries have set against American goods. “Very simply, it’s if they charge us, we charge them,” the President said on Sunday during a flight on Air Force One.