China's embassy in Britain on Sunday condemned a visit this week by British lawmakers to Taiwan, saying they were insisting on visiting the island despite China's strong opposition.
Taiwan's Presidential Office said the group of six lawmakers from the British-Taiwanese All-Party Parliamentary Group would meet President Tsai Ing-wen in Taipei on Monday.
China views democratically governed Taiwan as its own territory and has been ramping up military, political and economic pressure to assert those claims.
A statement from China's embassy in London said that the lawmakers have "insisted on visiting the Taiwan region of China despite China's resolute opposition".
This is a "gross interference in China's internal affairs and a serious wrong signal to Taiwan independence separatist forces," the embassy said.
"We want to tell the relevant British politicians that any act that harms China's interests will definitely be vigorously countered by China," it added, without elaborating.
Taiwan regularly hosts visiting foreign lawmakers, which China routinely condemns.
Taiwan's government rejects China's sovereignty claims, saying only Taiwan's people can decide their future.