A Koch In dustries executive was told he could not leave China . An ex-diplomat who helped organize a technology forum in Beijing was hassled by authorities who wanted to question him . An industry group developed contingency plans, in case its offices were raided and computer servers were seized.

Business executives, Washington officials and other frequent visitors to China who were interviewed by The New York Times expressed increasing alarm about the Chinese authorities’ harassment of Americans by holding them for questioning and preventing them from leaving the country.

They worry that trade tensions between Washington and Beijing could turn businesspeople and former officials into potential targets. Some companies are reviewing or beefing up their plans in case one of their employees faces problems, three people said. Many of the more than a dozen people interviewed by The Times asked for anonymity because they feared reprisals from the Chinese authorities.

“In a very not-so-subtle manner, the Chinese government has upped the ante by detaining Americans at the borders and at their hotels, and with the obvious intent to send a message to the Trump administration that they can engage in hostage diplomacy if push comes to shove,” said James Zimmerman, a partner in the Beijing office of the law firm Perkins Coie, which works with American companies in China.