Minefield.

Reuters/Thomas White

Vietnam has fought Chinese territorial claims over the South China Sea on t-shirts and in a movie. Its latest battleground is phones and cars.

Hanoi plans to inspect pre-installed navigation apps on Chinese smartphones such as Huawei and Xiaomi to make sure the maps used by their navigation apps do not include China’s controversial ”nine-dash line,” Bloomberg reported recently, citing Vietnam’s Tuoi Tre newspaper. Since October, Vietnam has also been barring models of Chinese cars for sale that come with navigation apps displaying that line, which China uses to lay claim to large swathes of the sea and its resources.

At a government press conference last week, officials said they were ordering businesses and universities—the offending line was also found in an imported textbook—to step up their checks to make sure products containing the map don’t make it into Vietnam, according to Vietnam Customs, a website under the country’s customs department. The country’s deputy trade minister said customs agents have been ordered to closely inspect maps and software in imported cars. Chinese carmaker Hanteng Autos saw seven of its car models impounded by Vietnam recently for the vehicles’ use of the disputed map, according to Tuoi Tre, while Volkswagen’s local distributor also landed in trouble for displaying a model that used such a map.

The nine-dash line, also known as “cow’s tongue” in China because of its shape, first appeared on an official Chinese map in the 1940s, and was adopted by Communist China. In 2016, an international tribunal ruled the line was essentially illegal, in response to a case brought by the Philippines. Despite the ruling, Beijing maintains it has rights within the U-shaped line, which encircles Taiwan—a self-governing democracy—as well as areas claimed by the Philippines, Vietnam, and Malaysia. In recent years, with Philippines leader Rodrigo Duterte taking a more conciliatory approach to China, some of the staunchest pushback to China’s claims has come from Vietnam.

The contested South China Sea.

Last month, Vietnam banned the screening of Dreamworks animated film Abominable, which contains the disputed line, while Jackie Chan, the popular Hong Kong movie star, had to cancel a charity event in Vietnam last week, after thousands of angry Vietnamese internet users flooded the Facebook page of the charity, accusing Chan of supporting China’s claims although he has never voiced support for the line explicitly.

Some private businesses in Vietnam have already started their own screening for the disputed map. A Vietnamese automobile distributor, which sells Chinese cars including Haima, Geely, Zotye, and Baic, said last month it would start to remove the default navigation map on those vehicles that include the nine-dash line.

The scrutiny puts Chinese companies in a difficult situation, as they try to please both domestic and overseas consumers—mirroring the tricky position of US firms doing business with China.

For now, companies are dealing with the situation by using different services in China and abroad. In the case of Huawei, the navigation apps its phones come with in China are from search engine giant Baidu or navigation service provider amap—those Chinese providers’ maps include the nine-dash line, according to their websites, even though it would never be used for navigational purposes by any user. Xiaomi also uses amap (link in Chinese) for its phones in China, according to its users.

The nine-dash line shows up on amap.

Meanwhile, in Vietnam, the two companies use Google maps that do not contain the line, according to marketing representatives from Xiaomi and Huawei who were quoted by Vietnamese news outlet Zing.vn. Huawei declined to comment, while Xiaomi did not reply to a request for comment. Both brands are relatively recent arrivals in the Vietnam smartphone market, though another Chinese smartphone maker, Oppo, is the second-biggest player after Samsung.

Having different practices in China and overseas, doesn’t mean Chinese companies are safe from ire in China. In August, Huawei came under fire for listing Taipei as “Taipei, Taiwan” in its region menu for users who choose traditional Chinese, used in Taiwan, as their written language. Beijing, which regards Taiwan as a “Chinese province,” sees that as implying the self-ruled island is a country. After Chinese internet users advocated a boycott of Huawei, the company quickly modified Taipei to show it as part of China for mainland users, while models outside of China list Taipei with no country after it.