The Trump administration is hitting back at a number of countries for what it considers unjustified retaliatory tariffs that were imposed as a response to the steel and aluminum duties the U.S. applied on its closest allies in the name of national security.

The U.S. Trade Representative said it launched formal challenges against China, the European Union, Canada, Mexico and Turkey at the World Trade Organization on Monday. They come in response to retaliatory measures taken by these countries on American-made products earlier this year.

“The actions taken by the President are wholly legitimate and fully justified as a matter of U.S. law and international trade rules. Instead of working with us to address a common problem, some of our trading partners have elected to respond with retaliatory tariffs designed to punish American workers, farmers and companies,” U.S. Trade Representative Robert Lighthizer said in an emailed statement.

Lighthizer said the U.S. would take “all necessary actions” to protect U.S. interests and urged trading partners to “work constructively” with the Trump administration to address overcapacity in both metal sectors.

A European Commission spokesman said that while the bloc’s decision to retaliate was proportionate and WTO-compatible, the U.S. is entitled to seek an independent review in which the European Union will explain and defend its position.

Canada, China, the EU, Mexico and Turkey have imposed retaliatory tariffs on $23.4 billion worth of U.S. goods in response to Trump’s tariffs on steel and aluminum.

The Trump administration has criticized the WTO for encroaching on U.S. legal sovereignty and failing to rein in China’s alleged violation of global trading rules. Trump himself threatened to take action against the WTO earlier this month after the Axios news agency reported that his administration had drafted legislation to withdraw the U.S. from the organization, a move the president repeatedly told advisers he was considering.

The WTO has“not worked well, or not as well as it was intended to work when China was brought into the WTO in the year 2000,” Treasury Undersecretary for International Affairs David Malpass said at an event in Washington on Monday.