"This is a mistake," said Rep. Carlos Curbelo (R-FL). "Tariffs should specifically and exclusively target countries that engage in abusive trade practices, not our friends and allies."
"Trade wars do not end well," said Sen. Jeff Flake (R-AZ), as many in both parties have expressed concerns about Mr. Trump's aggressive trade actions.
"In addition to higher prices, these tariffs invite retaliation," said Sen. Pat Toomey (R-PA).
Retaliatory tariffs were immediately announced by Mexico, targeted mainly at American agricultural products, while in Europe, EU leaders made clear they would respond as well.
"It's a bad day for world trade," said Jean-Claude Juncker, the head of the European Union.
"We will defend the EU’s interests, in full compliance with international trade law," he added.
Mr. Trump's move came two days after the White House signaled that it would move ahead with $50 billion in tariffs on a variety of goods imported from China.
Commerce Secretary Wilbur Ross denied that this was the start of a trade war.
"No, not at all," Ross said in an interview on CNBC. "As you know, this has been under discussion for quite a long time, and it's a very small percentage of the respective economy."
The Trump Administration argues that these new tariffs are being used for one main purpose - to force open markets for U.S. exports, and reduce what the President has long said are unfair trade barriers which hurt American exports, as officials routinely cite issues on the table in NAFTA trade negotiations with Canada and Mexico.
"The Section 232 steel and aluminum tariffs have already had major, positive effects on steel and aluminum workers and jobs and will continue to do so long into the future," the White House said in a statement.
"At the same time, the Trump Administration’s actions underscore its commitment to good-faith negotiations with our allies to enhance our national security while supporting American workers," the statement added.
"Trump's trade policy: punish US allies, Canada, Mexico, EU while cutting a special deal for China's ZTE," said Rep. Gerry Connolly (D-VA). "Making America retreat again."