Calls in South Korea for a boycott of Japanese goods in response to Tokyo’s curbs on the export of high-tech material to South Korea picked up on Friday, as a dispute over compensation for forced wartime labor roiled ties between the U.S. allies.

It is the latest flashpoint in a relationship long over-shadowed by South Korean resentment of Japan’s 1910-1945 occupation of the Korean peninsula, in particular South Korean “comfort women”, a Japanese euphemism for women forced to work in Japanese military brothels before and during World War Two.

Japan apologized to the women as part of a 2015 deal and provided a 1 billion yen ($9.4 million) fund to help them.

Advocacy groups for the women have criticized the fund and South Korea dissolved it on Friday, despite Japan’s warnings that such action could damage ties.

“This is totally unacceptable for Japan. We’ve made stern representations to the South Korean side,” Deputy Chief Cabinet Secretary Yasutoshi Nishimura said in Tokyo.

The bitterness over the forced labor issue could disrupt global supplies of memory chips and smartphones.

Japan said on Monday it would tighten restrictions on the export of high-tech materials used in smartphone displays and chips to South Korea. The curbs took effect on Thursday, fuelling South Korean calls for retaliation.

Samsung Electronics Co (005930.KS) and SK Hynix Inc (000660.KS) – the world’s top memory chipmakers, and suppliers to Apple (AAPL.O) and China’s Huawei Technologies HWT.UL – could face delays if the curbs drag on.

“A boycott is the most immediate way for citizens to express their anger,” said Choi Gae-yeon of the activist group Movement for One Korea, that staged protests in front of a Japanese car showroom and a retailer in Seoul this week.

“Many people are angry at the attitude of the Japanese government,” she said.

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