Ford cars and California fruits are among the goods piling up at Chinese ports, the result of increased inspections that business groups say is China’s way of reminding the U.S. how important its market is to American exporters. Navel oranges, lemons and cherries from California, along with American apples, have been sitting at Chinese wharves for longer than normal as Chinese inspectors spend more time inspecting the fruits for pests and decays, U.S. trade groups said. Ford Motor Co. vehicles are likewise being subjected to unusually rigorous checks at the port, people familiar with the matter said. Pork is also coming under more frequent inspections, U.S. officials say, as U.S.-China trade tensions show no signs of easing.The Chinese “are trying to identify industries or sectors that could put pressure on the administration to change its posture,” said Joel Nelsen, president of trade association California Citrus Mutual. He said inspectors are opening and sifting through most of the 900 cartons of citrus fruit in each shipping container. William Zarit, chairman of the American Chamber of Commerce in China, said China appears to be following a tried-and-true playbook.“China basically speaks with one voice on trade. It’s not that difficult for the (Communist) party to send out an order and it will happen very quickly—and for the most part, systematically and consistently,” Mr. Zarit said. Last year, amid tensions about South Korea’s deployment of a U.S.-built missile-defense system, China stopped sending tour groups to the country and sales of Hyundai Motor Co. cars in China plummeted. China at one time imposed curbs on imports of Philippine bananas over rival territorial claims in the South China Sea. China’s General Administration of Customs didn’t immediately respond to a request for comment. Geng Shuang, a Foreign Ministry spokesman, said he wasn’t aware of any effort to restrict U.S. imports. “In principle,” Mr. Geng said Thursday, “China carries out relevant inspection and quarantine work in accordance with laws and regulations following a scientific and unbiased method.” Fruit is an easy target in a trade dispute as its passage through customs can easily be delayed on health and safety grounds, an official at a southern Chinese port said. China’s customs agency said Monday it would start strengthening quarantine inspections on U.S. apples and timber after claiming to have found pests in some recent shipments. Before last week, U.S. cherries could pass through such quarantine inspections in a matter of hours, said Keith Hu, director of international operations at Northwest Cherry Growers in Washington state. Mr. Nelsen, of California Citrus Mutual, said oranges and lemons would typically take a couple of days to clear the reviews. Now the process is, in some cases, taking five to seven days.