China's warning about traveling in U.S. — the latest shot amid the worsening trade war — could pose a threat to some airlines and casinos, although the overall impact on U.S. tourism would be manageable.

While Chinese tourists spend heavily around the world, contributing to $270 billion abroad last year alone, they only accounted for 3% of the $1.1 trillion U.S. travel market in 2018, according to the U.S. Travel Association. In a worst-case scenario, the number of Chinese tourists to the U.S. could drop by nearly 50%, resulting in an $18 billion hit to travel spending, Bank of America Merrill Lynch estimated.

"Chinese tourism is a big prize in global trade. ... On this front, the U.S. has more to lose than China," Robin Winkler, foreign exchange strategist at Deutsche Bank, said in a note. The trade war "would likely take a severe dent to household income growth to squash the new middle class's appetite for passports and foreign travel. A weaker exchange rate could make foreign travel somewhat less affordable," Winkler added.

Chinese travel to the U.S. has already declined by 5.7% in 2018 from a year earlier, compared with a 4% gain in 2017 and a 15% increase in 2016, according to the U.S. Travel Association. The number is only going lower after the Chinese government issued an alert for Chinese tourists traveling to America, citing "shootings, robberies and theft" that have occurred "frequently" in the U.S.