BEIJING — Kai Li, an American businessman born in China, had stepped off a plane in Shanghai, preparing to visit his mother’s grave. Instead, Chinese state security officers grabbed him and accused him of spying, and a court later sentenced him to 10 years in prison after a short, secretive trial.
Now, two and a half years after Mr. Li was detained, his family in New York has broken its silence, saying that the espionage conviction against Mr. Li, an exporter of aircraft parts, was groundless and driven by political motives.
In recent years, relations between the United States and China have been tested by trade and technology disputes. The United States has accused China of hacking companies and inducing or bribing scientists to hand over commercial secrets. China has also stepped up warnings against foreign spies and publicized convictions of foreigners on espionage charges.
Harrison Li, Mr. Li’s son, said the Chinese authorities had charged his father with providing state secrets to the F.B.I. He says he is sure that his father was not a spy, and that his conviction showed the risks that American visitors to China face as tensions with the United States have festered.
“I certainly hope that the U.S. government will view my father’s case as a serious indication of China’s willingness to use the coercive and inflammatory tactics of detaining foreign citizens,” Harrison Li said by telephone. “It’s very clear to us that the nature of the case is political, and tied to whatever geopolitical conflicts exist between the two countries.”
At first, Mr. Li’s family kept quiet about his case while State Department officials lobbied Chinese officials to release him, the son said. But Mr. Li, 56, went on trial in Shanghai in August 2017 and was convicted and sentenced in July of last year. Harrison Li said that he and his mother decided to speak out after Mr. Li’s appeal was rejected last month.
The F.B.I. declined to comment on the case. The Chinese Ministry of Foreign Affairs did not respond on Friday to faxed questions about the case, nor did the police, the prosecutors’ office or the foreign affairs office in Shanghai.
The case raises broader questions about how foreign businesspeople dealing with sensitive sectors in China — in this case, the aerospace sector — are vulnerable to espionage charges.
Before Mr. Li’s detention, his life centered on his home and businesses on Long Island, where he owned two gas stations. He had migrated to the United States in 1989 and gained citizenship there in the 1990s, said his son, who works in finance. Mr. Li’s wife also migrated from China.
Mr. Li visited China two or three times a year, and he ran a company that exported aircraft parts to China and elsewhere in Asia on behalf of a subsidiary of Boeing, Harrison Li said.
The aerospace sector looms large in the competition between China and the United States, and both governments guard against the theft of secrets. Last year, the United States orchestrated a complex international sting operation to arrest a Chinese intelligence official who was charged with trying to get proprietary information from a GE Aviation employee.
“I’m sure that his business would have made him an easier target for the Chinese government,” Harrison Li said of his father. He said his father wrote in a letter, while in detention, that the paperwork for the exports entailed making filings with the United States government that may have drawn suspicion from Chinese investigators.
Mr. Li’s case has added to the tensions between Beijing and Washington.
Relations have been strained since last year, when President Trump hit goods made in China with tariffs intended to force Beijing into dismantling what he and other critics say are unfair trade and investment barriers.
China was also incensed by the arrest in Canada late last year of Meng Wanzhou, the chief financial officer of Huawei, who American prosecutors say helped Huawei slip past American sanctions on Iran by fraudulently misleading a bank. Two Canadian men were detained in China in December in what appeared to be payback for Ms. Meng’s arrest.
“The international security competition between the United States and China is beginning to affect the business world in a very significant way,” said Evan S. Medeiros, a professor at Georgetown University who was senior Asia director in the Obama White House.
In targeting American businesses, China has a “much bigger tool kit to play with” because of the vast powers of its state security apparatus and lack of real legal oversight, Mr. Medeiros said, without commenting specifically on Mr. Li’s case.
Members of the Trump administration and of Congress have taken up Mr. Li’s case, including Secretary of State Mike Pompeo and other State Department officials, Harrison Li said.
“We regularly raise Mr. Li’s case with Chinese officials,” the State Department said a written statement. It said consular staff had sent multiple requests to the Chinese authorities seeking Mr. Li’s release on humanitarian grounds, but received no response.
This week, Senator Chuck Schumer, a Democrat from New York, sent a letter to Mr. Trump urging him, for a second time, to push the Chinese government to release Mr. Li.
“The Trump administration must use all tools available to prioritize bringing Mr. Li back home,” Mr. Schumer told The Times on Thursday.
In recent years, Chinese security officers have been especially tough in detaining people born in China who have foreign citizenship. Some visitors of Chinese descent have spent years in prison on sweeping charges.
In a travel warning for China issued last month, the State Department said that American citizens of Chinese heritage could face additional scrutiny and harassment.
When Mr. Li went to trial, United States consular officers were not allowed into the hearing, after the court invoked a rule banning outsiders from sensitive cases involving national security. The hearing lasted a little over an hour, said Harrison Li, who is in touch with the consular officers.
After the trial, the court took the unusual step of ordering additional investigation by the prosecution office, postponing a judgment, Harrison Li said. Such a move suggests that judges thought the evidence presented by the prosecution was insufficient.
Still, the judges last year declared Mr. Li guilty of sharing one “classified” state secret and four “confidential” state secrets, his son said, citing a judgment seen by the United States consulate in Shanghai. Those classes of secrecy both fall below the topmost confidentiality classification in China.
Harrison Li hopes that Mr. Trump will take up his father’s case when he next meets with Mr. Xi. But he said he had qualms about speaking out because he was afraid that the authorities might take it out on his father, who has been in poor health with bouts of shingles and constant stomach ailments.
“There’s already a very real concern that when families of imprisoned people in China go public, they retaliate,” he said. “It just seems that there’s not much more that can be done quietly.”