American Airlines
American Airlines aircraft are parked at Ronald Reagan Washington National Airport in Washington, Aug. 8, 2016. REUTERS/Joshua Roberts

The three biggest United States airlines changed how they refer to self-ruled Taiwan on their websites in an effort to avoid Chinese penalties by a Wednesday deadline.

Beijing has demanded that foreign firms, and airlines in particular, not refer to Taiwan as a non-Chinese territory on their websites, a move described by the White House in May as "Orwellian nonsense."

China set a final deadline of July 25 for the changes, and last month rejected U.S. requests for talks on the matter, adding to tension in relations already frayed by an escalating trade conflict.

Taiwan is China's most sensitive territorial issue. Beijing considers the island a wayward province of "one China."

Reuters reported early on Tuesday that American Airlines Group Inc, Delta Air Lines and United Airlines were set to change how they refer to Taiwanese airports on their websites. American Airlines confirmed the change later in the day.

A check of all three airlines' websites on Wednesday morning showed they now only list Taipei's airport code and city, but not the name Taiwan.

Taiwan's foreign ministry on Wednesday said it "most severely" condemned the Chinese government's use of political power to "crudely and unreasonably interfere with private commercial activity and international companies' operations".

It was unclear how China might punish airlines that do not comply, but in December it added a clause to rules governing foreign airlines saying regulators could change a company's permit if it did not meet "the demand of public interest".

American Airlines spokeswoman Shannon Gilson said the firm had implemented the changes at China's request in line with other carriers. "Air travel is global business, and we abide by the rules in countries where we operate," she said on Tuesday.

Hawaiian Airlines had changed its website ahead of the deadline to showing searches for flights to Taiwan's capital Taipei as "Taipei, Taipei" in dropdown menus, Reuters reported on Tuesday morning.

The U.S. State Department and White House did not immediately respond to requests for comment late on Tuesday.

Numerous non-U.S. airlines including Air Canada, Lufthansa and British Airways had already made changes to their websites, according to Reuters checks, after China's Civil Aviation Administration sent a letter to 36 foreign air carriers earlier in the year.