The one-month exemption to 25% tariffs on vehicles and auto parts will be a big challenge for car companies to reset supply chains, say experts.

The leaders of both Canada and Mexico got on the phone with President Donald Trump this past week to seek solutions after he slapped tariffs on their countries, but China’s president appears unlikely to make a similar call soon.

The tariff actions, which could upend nearly $2.2 trillion in two-way annual U.S. trade, went live hours after Trump declared that all three countries had failed to do enough to stem the flow of the deadly fentanyl opioid.