Inevitably, I can't find it simply spelled out on a government website, but the practice up to now has been that engineers can come to USA to under the visa wai

Inevitably, I can't find it simply spelled out on a government website, but the practice up to now has been that engineers can come to USA to under the visa waiver program to service or install machinery. From an immigration law firm: "Citizens of many foreign countries, including most European citizens, may travel as tourists or on business under the U.S. Visa Waiver Program without any formal visa application, and only registration under the Electronic System for Travel Authorization (ESTA) is required. Under the program, a European executive may visit a corporate subsidiary or attend a trade fair. Similarly, when specifically required by the purchase contract, technical experts who have to travel to the United States to install, service or repair equipment or machinery sold by a foreign company to a U.S. buyer can travel under the Visa Waiver Program. Travel for technicians and engineers installing foreign-made equipment in the United States is limited to a maximum of 90 days per stay and has to be in performance of a contract of sale of foreign equipment to the United States requiring installation (or repair service under warranty) at the customer site. The installation cannot include construction work, except for supervision or training of U.S. workers to perform construction". https://www.sgrlaw.com/ttl-articles/foreign-manufacturers-traps-for-the-unwary/ https://www.sgrlaw.com/ttl-articles/foreign-manufacturers-tr... Presumably the ICE officers applied this test before detaining each of the Hyundai workers.....