Chinese regulators appear to have rejected a possible attempt by US airlines at a compromise over Beijing's demand to call self-ruled Taiwan a part of China, an order Washington opposed.
The communist mainland's latest effort to use China's growing economic clout to isolate Taiwan's democratically elected government is further straining ties between Beijing and the US amid a deepening trade dispute.
The Chinese airline regulator says United Airlines, American Airlines, Delta Air Lines and Hawaiian Airlines missed a Wednesday deadline to change their websites while 40 other carriers obeyed.
Taiwan and China separated in 1949 following a civil war on the mainland but Beijing claims the island, formally known as the Republic of China, as part of its territory.
The US airlines made some changes "but rectification of the content still is incomplete," the Civil Aviation Administration of China said on its website. It gave no details and phone calls to the agency weren't answered.
Beijing demanded airlines call Taiwan's capital "Taipei, China." Three of the US carriers cited by CAAC switched to saying only Taipei, with no country, on their websites. Other destinations have city and country names.
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"We complied within the deadline with what we thought was a nice solution for everyone," American Airlines chairman Doug Parker said in a conference call this week to discuss the airline's financial results.
The Trump administration rejected the order in May as "Orwellian nonsense" and expressed dismay that airlines obeyed.
Other airlines including British Airways, Air Canada and Lufthansa started using "Taipei, China" to avoid Chinese penalties.
Hawaiian Airlines doesn't fly to Taiwan. It has a code-sharing agreement with Taiwan's China Airlines but its website has no mention of Taipei.
Last week, an airline from the Pacific nation of Palau said it shut down due to a drop in tourism from China. Chinese officials last year reportedly told tourist agencies to stop booking trips to Palau to punish the tiny nation for having diplomatic ties with Taiwan.
In January, hotel chain Marriott was ordered to shut down its China website and app for a week after it sent out a customer survey that included Taiwan, Tibet and Hong Kong in a list of countries. News reports said Marriott executives were questioned by police.
The government also criticized fashion brand Zara and other countries for referring to Taiwan as a country on their websites.