"The European Union has concocted a groundless legal theory to justify immediate tariffs on US exports," Lighthizer said on Tuesday.
Earlier, Washington announced it would impose tariffs on steel imports and 10 percent on aluminum imports on the European Union, Mexico, and Canada beginning from June 1.
READ MORE: Harley-Davidson Move Shows US Facing 'Consequences' of Tariffs – EU
Brussels expressed its opposition to the US tariffs. European Commission President Jean-Claude Juncker has called the US move pure protectionism, and said that the bloc would retaliate with its own duties, and complain to the World Trade Organisation (WTO) over the US trade policies.