Chinese authorities are again shaking the confidence of foreign companies in the country with a series of arrests and an investigation into Foxconn Technology Group, Apple’s most important partner and one of the largest employers in China.

Over the weekend, state media said that regulators are conducting tax audits and reviewing land use by Foxconn, the Taiwanese company that makes the vast majority of iPhones at factories in China. Hon Hai Precision Industry, Foxconn’s public arm, said it will collaborate with authorities.

Meanwhile, an executive and two former employees of WPP, one of the world’s biggest advertising companies, have been arrested in China, people familiar with the matter have said. In March, the government detained a local employee of a Japanese metals trading company on suspicion of leaking information. And this month, a court formally charged an Astellas Pharma employee on suspicion of espionage.