Unite's national officer for steel, Tony Brady, added that a 30-day respite from the tariffs was "not the answer".
The U.S. and China are the world's largest economies, respectively.
"Very much like North Korea, this should have been fixed years ago, not now", he said Tuesday of the United States' wide trade deficit with China.
Trade ministers from the three countries met last week to advance talks on revising the 24-year-old NAFTA and made enough progress that they have set their next ministerial meeting for May 7.
It's not surprising that Mexico and Canada were granted extensions ahead of the next round of NAFTA talks scheduled for May 7, according to Height Capital Markets.
Canada is the biggest steel exporter to the US.
Previously at a briefing in March, Davies said the tariffs would be a risk for local jobs, particularly in the aluminium industry. Security relationships with the US have also been part of the criteria.
The EU had consistently shown it was willing to discuss concerns about the openness of each other's markets, but would not negotiate under threat, the Commmission said.
Lighthizer said it would be "madness" for the United States to keep allowing Chinese-state backed firms to buy up USA technology companies, especially as China prohibits such acquisitions by US firms. "Fundamentally, the German government's expectation remains a permanent exemption".
Such limited tariffs would not impact Finland very much however, as only two percent of its exported steel and aluminium ends up on the United States market.
Trump administration officials have said that in lieu of tariffs, steel-and aluminium-exporting countries would have to agree to quotas created to achieve similar protections for U.S. producers.
Germany and France are among the main European Union countries to support the permanent exemption.
Prior to the deadline switch, South Korea had already been granted a permanent exemption from the tariffs by reaching a final deal with the White House.
The dispute comes as Washington seeks to stave off a separate trade conflict with China.