The sighs of relief for European and Japanese carmakers after Donald Trump’s expected decision to delay imposing punitive tariffs may prove premature.

The U.S. president is poised to give the EU and Japan 180 days to agree to a deal that would “limit or restrict” imports into the U.S. of automobiles and their parts, according to a draft executive order seen by Bloomberg. The problem is that Trump’s plan concludes that car imports do in fact constitute a national-security threat, and what he’s seeking in return for a tariff reprieve may not fly.

World Trade Organization rules prohibit any voluntary export restraints. The European Union, and especially countries like France, says it opposes any deal with the U.S. that would violate WTO rules and the international rules-based order.

Optimists may hope that European powers which are most keen to avoid car tariffs, such as Germany, could convince the bloc to turn a blind eye to potential WTO violations with export restrictions. The bloc was ready to accept afudged deal of this kind last year, when Trump threatened the EU with punitive tariffs on steel and aluminum.

In a last-ditch attempt to avoid the levies, the EU signaled it was willing to tolerate quotas. This means that it wouldn’t legally challenge or retaliate potential tariffs on steel and aluminum, as long as these were imposed after a certain volume of exports.

In practice, what Trump was demanding and what the EU was willing to tolerate proved impossible to reconcile. U.S. tariffs on steel and aluminum were eventually imposed, and the EU retaliated with duties on a long list of U.S. goods ranging from motorcycles to bourbon.

The difference between last year’s trade brawl is that this time around the EU and the U.S. are formally negotiating a trade accord to cut tariffs on industrial goods and they have said they won’t impose additional levies while talks are moving. But ongoing negotiations with Beijing didn’t stop Trump from imposing additional levies against China, and judging from the president’s previous comments comparing the EU and China, there’s no guarantee he’ll treat his western allies any differently.

European carmakers Thursday gave up gains following the decision to delay tariffs. Volkswagen AG, maker of the Porsche and Audi brands, fell 0.9% after rising as much as 5.7% Wednesday. Daimler AG and BMW AG also declined, 0.8 percent and 0.2% respectively after rising by a similar amount the day before.