Japan's two largest airlines have changed "Taiwan" to "China Taiwan" on their Chinese-language websites, officials said on Tuesday, sparking an immediate protest from the self-ruled island.
China, which claims Taiwan as its own territory, has demanded that dozens of international airlines make such a change despite US protests at what it called "Orwellian nonsense".
Japan Airlines (JAL) and All Nippon Airways (ANA) said their alteration was made on June 12 and was meant to accommodate customers.
The description remains "Taiwan" on their websites in Japanese and other languages.
"We made the judgement (to change the name) while consulting and reporting to the transport ministry and foreign ministry," said a spokesman at Japan Airlines.
"The change came on June 12 as our preparations were done by then," he said.
June 12 was the date of the historic summit between North Korea and the United States, which attracted international attention.
"We chose a description that is easy to understand and acceptable for users of our websites," added the JAL official.
A spokesman at ANA said the change was intended to make the description "easy to understand and acceptable for customers when they use our websites".
"We do not mean any particular group of customers here but mean all customers," he said without elaborating.
Taiwan's foreign ministry said it was lodging protests with the two airlines and demanded a correction to the "inappropriate title".
"Chinese authorities once again are unreasonably pressuring Taiwan's international space," the ministry said, adding that such moves "only increase resentment among Taiwanese people and severely harm cross-strait relations".
The airlines are not the only international carriers who have made the change recently, with Australia's Qantas earlier this month defending its decision to list Taiwan as part of China.
The Chinese Civil Aviation Administration sent a notice to 36 foreign airlines in April, asking them to comply with Beijing's standard of referring to Taiwan, Hong Kong and Macau as Chinese territories.
Japan's ties with China are improving after years of acrimony over historical and territorial issues.
Japan has close business ties with Taiwan but has acknowledged the "One China" policy, which describes the island as an integral part of China.
Asked about the change, Japan's top government spokesman Yoshihide Suga said Tokyo was "not in favour of government authorities demanding certain measures from private companies based on a specific political stance".