US President Donald Trump announced on Wednesday 25% tariffs “on all cars that are not made in the US” effective 12.01am eastern time on April 3.
“We have to think about appropriate measures following this announcement. Naturally, we will consider all options,” Ishiba told parliament.
“Japan has made significant investments and significant job creation, which doesn’t apply to all countries… We are the number one (country) in investment in the US,” Ishiba added.
“The US president’s understanding on this is significantly deepening. However, various things are happening, so we are considering all kinds of countermeasures, and those exist as our options.”
Trump’s announcement sent shares in Japanese auto giants down sharply on Thursday.
The world’s top-selling automaker Toyota was down almost 3.5%, while Nissan shed 2.5% and Honda fell as much as 3.1%.
Mitsubishi Motors was down 4.5%, while Mazda fell 5.9% and Subaru 6.1%.
In South Korea, Hyundai shares dipped 2.7%.
The auto industry is a huge pillar of the Japanese economy, with about 10% of jobs there connected to the sector.
Vehicles accounted for roughly a third of Japan’s 21.3 trillion yen (US$142 billion) of US-bound exports in 2024.
Earlier in March, the chair of the Japan Automobile Manufacturers Association (JAMA) warned of the impact of US trade protectionism at a Tokyo press conference.
A 25% tariff “would have a negative impact overall on the economies of the US and Japan”, Masanori Katayama said.
Japanese ministers have been lobbying their US counterparts to secure tariff exemptions for goods like steel and vehicles, but these requests have been denied.
The Trump administration says levies are a way to raise government revenue, revitalise American industry and press countries on US priorities.
But targeting imported cars could strain ties with close US partners.
About 50% of cars sold in the US are manufactured within the country. Among imports, about half come from Mexico and Canada, with Japan, South Korea and Germany also major suppliers.