Three major Chinese EV companies are planning to build new factories in Mexico, sparking concern among US officials, according to a new report.

MG, BYD, and Chery are all looking at sites to build new factories in the country, according to unnamed sources cited by The Financial Times, and this investment is causing angst in Washington as it seeks to keep China out of the US electric car market.

US officials have reportedly raised concerns with their Mexican counterparts over Chinese investment, with the new sites potentially including a new $1.5 billion to $2 billion MG electric car factory and a factory investment worth hundreds of millions of dollars from Warren Buffett-backed Tesla rival BYD.

China’s electric vehicle market is booming, and local manufacturers are increasingly looking to expand overseas amid cutthroat competition for customers back home.

China also dominates the global electric vehicle battery supply chain, allowing it to produce far cheaper EVs than many of its US rivals.

The US has attempted to protect the US market by unveiling new rules earlier this month to make it more difficult for EVs made with Chinese parts to qualify for tax breaks.

But the possible expansion of Chinese automakers into Mexico, which recently replaced China as the US’ biggest trading partner, will fuel fears that it could serve as a backdoor.

Lawmakers on a select committee on China recently warned that stronger trade rules may be needed to prevent Chinese automakers from “gaining a backdoor to the US market” through its trading partners.

Mexico has proven a tempting target for carmakers in recent years, thanks to its low labor costs and a free-trade agreement with the US.

Tesla is planning to build a gigafactory near Monterrey, where it is expected to produce its long-awaited $25,000 electric car.

BYD, MG, and Chery did not immediately respond to a request for comment from Business Insider, made outside normal working hours.