Japanese telecom giant SoftBank might become a target for Uber Inc’s aggresive executives after it invested $250 million into the citizen taxi service’s biggest rival in Southeast Asia – a startup called GrabTaxi.

The GrabTaxi app has seen massive growth in Southeast Asia, and is now Uber’s biggest rival in the region. With SoftBank’s backing, the company is likely to try to expand its service further, hampering Uber’s own plans to establish itself in the region.

Although they’re rivals, the two services are also quite different. While Uber has its own network of drivers that offer “lifts” to passengers, GrabTaxi works with registered taxis to connect them with passengers. It’s a strategy that seems to be working in Asia, where taxi fares are considerably cheaper than those in the U.S. More important, perhaps, is that by working with registered taxis, GrabTaxi has managed to avoid the regulatory problems that Uber is currently facing.

Since its launch in 2012, GrabTaxi has expanded to serve 17 cities in Singapore, the Philippines, Thailand, Vietnam, Indonesia and Malaysia. It claims around 500,000 users per month and says it has more than 60,000 taxi drivers signed up.

But despite SoftBank’s investment, GrabTaxi isn’t looking to expand its business outside of its home base just yet. Speaking to TechCrunch, GrabTaxi CEO Anthony Tan said he was hoping to “grow very fast and focus on expanding in this region.”

SoftBank’s investment means it becomes GrabTaxi’s largest backer to date, and the company said it’s funding will be used to help the firm build its presence in Southeast Asia and “maximize synergies” with its expanding network of Internet companies.