Asian nations are not taking President Trump’s 30% tariffs on imported solar cells and modules lying down.

Only one day after the tariffs were announced in late January, Korean trade authorities pledged to file a petition through the World Trade Organization (WTO) to ensure that the nation could “protect its national interests”, particularly as relates to the more than $1 billion in solar cells and modules that the nation exports to the United States each year.

Today Korea made good on its promise, filing a notice with the WTO seeking permission to file for “substantially equivalent” retaliatory trade sanctions on U.S. goods, for as long as the Section 201 tariffs last.

Japan has filed a similar notice. The nation did not state the value of its exports to the United States.

WTO rules allow nations to impose retaliatory and equivalent trade sanctions if it finds that the measures taken by the United States are not in compliance with WTO rules. Such retaliatory measures led President Bush to repeal the last set of global safeguard tariffs by the United States in 2002 on steel products, less than two years after they were imposed.

This is far from the only challenge to the Section 201 tariffs to come from an international government. Canadian companies have sued to exempt their products from the tariffs, and Mexico has threatened legal action as well.

The move by Japan and Korea comes only days after China threatened $50 billion on tariffs on U.S. goods, including agricultural products, aircraft and automobiles in retaliation for Trump’s proposed 25% tariff on a list of Chinese goods under the Section 301 process.

The list of over 1,000 potential targets for tariffs under Section 301 includes some parts for batteries, but did not include solar cells, modules, inverters, or the lithium-ion batteries used to accompany solar PV or in electric vehicles.