World Trade Organization

Updated at 8:15 a.m. ET

As the day dawned across the U.S. on Friday, a new economic reality dawned with it: The tariffs long threatened against billions of dollars in Chinese goods took effect just at midnight ET while many Americans were sleeping — but Beijing was ready immediately with a wake-up call of its own.

After U.S. tariffs on imports of European steel and aluminum took effect Friday morning, the EU's top trade commissioner called them "illegal" and a classic case of protectionism.

The EU plans to make its case to the World Trade Organization.