Ahead of the historic meeting between the leaders of North and South Korea on April 27, 2018, political emblems depicting unity have been rolled out across South Korea.
One of these is an outline of the full Korean Peninsula, like on the Korean unification flag seen prominently at the Olympics. Inside Peace House, where Kim Jong Un and Moon Jae-In will meet, chairs have been engraved with the same outline and a miniature version of the flag will be placed on a dessert later in the day.
But not everyone views the symbols favorably.
The Korean unification flag features a set of disputed islands between Japan and South Korea that have been a source of tension for over a millennia.
Both South Korea and Japan claim the pair of nearly uninhabitable islets located in the Sea of Japan, which are controlled by South Korea. South Korea refers to the islands as Dokdo, while the Japanese refer to them as Takeshima.
Internationally, they have been given the name of Liancourt Rocks to avoid dispute.
Japan claims it acquired the islands in 1905 as terra nullius during its occupation of Korea, while Korea maintains it was illegally occupied and that Japan’s claims to the islands amount to continued imperialism.
The islands holds significant symbolic importance to South Korea but Japan has protested the use of the islands in the Korean unification flag.
On April 25, 2018, Japan’s foreign ministry lodged a formal complaint about the use of the flag, which is set to be featured on top of a mango mousse served during the inter-Korean summit on April 27, 2018.
A Japanese official met with the South Korean embassy in Tokyo, telling them the use of the flag is “deeply regrettable and unacceptable for Japan,” according to NHK News.
The Japanese Embassy in Seoul has also lodged a complaint with South Korea’s foreign ministry.
This is not the first time the symbol has angered Japan.
In February 2018, Japan lodged a protest against the unification flag which was on display during a women’s ice hockey match between the joint North-South Korean team and Sweden.
South Korea later said it would not depict the islands on the flag it intended to use during the Olympics. But pictures of North Korea’s cheerleaders at the games show they appear to have used the controversial flag anyway.
This article originally appeared on Business Insider. Follow @BusinessInsider on Twitter.