Japan says it is considering joining the US in filing a complaint with the World Trade Organization against China.
Japan is investigating whether it should back the US complaint
It is concerned over claims that China, its largest trading partner, gives national firms preferential taxes, giving them an unfair advantage.
The US has already complained to the WTO that China is essentially subsidising some of its industries.
Washington argues this means US firms cannot compete fairly and last week started legal action against China.
Japan said it was now trying to find out more about the claims after the issue was raised by US trade representative Susan Schwab.
"Based on our findings we hope to decide as soon as possible whether to join (the US complaint) as a third party." said Akira Amari, Japan's minister for economy, trade and industry.
Last week, Ms Schwab said China used tax legislation to "encourage exports and discriminate against imports", and called for a "level playing field".
Industries including IT, steel and paper are among those effected by China's stance, says the US.
Japan depends on China as a centre for manufacturing and, as the Chinese become richer, as a market for its consumer electronics.
Analysts observed that the US's stance against China came shortly after the Democrats, who have historically been more critical of Chinese trade policies, took power in Congress.
The US is due to enter bilateral talks with China and could then go to the WTO settlement panel.