(Bloomberg) -- China plans to expand a ban on the use of iPhones in sensitive departments to government-backed agencies and state companies, a sign of growing challenges for Apple Inc. in its biggest foreign market and global production base.

Several agencies have begun instructing staff not to bring their iPhones to work, people familiar with the matter said, affirming a previous report from the Wall Street Journal. In addition, Beijing intends to extend that restriction far more broadly to a plethora of state-owned enterprises and other government-controlled organizations, said the people, who asked not to be identified discussing a sensitive matter.

If Beijing goes ahead, the unprecedented blockade will be the culmination of a yearslong effort to root out foreign technology use in sensitive environments, coinciding with Beijing’s effort to reduce its reliance on American software and circuitry. It threatens to erode Apple’s position in a market that yields about a fifth of its revenue, and from where it makes the majority of the world’s iPhones through sprawling factories that employ millions of Chinese.

It’s unclear how many companies or agencies could eventually adopt restrictions on personal devices, and there’s been no formal or written injunction as yet, the people said. State firms or organizations will likely vary in how strictly they enforce such bans, with some forbidding Apple devices from the workplace while others could bar employees from using them entirely.

Chinese state firms like oil giant PetroChina Co. employ millions and control vast swathes of a centrally planned economy. Given Apple’s relationship with Beijing and its importance to the economy, it “has historically been viewed as relatively safe in China from government restrictions,” KeyBanc Capital Markets analyst Brandon Nispel said in a report Wednesday. “Is the government changing its stance?”

A representative for Cupertino, California-based Apple didn’t respond to a request for comment. The State-Owned Assets Supervision and Administration Commission and the State Council Information Office didn’t respond to faxed requests for comment.

Apple shares fell 2.9% Thursday in New York, following a 3.6% decline on Wednesday — their biggest single-day drop since Aug. 4. European chipmakers, including Apple supplier STMicroelectronics NV, also declined on Thursday.

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Apple enjoys widespread popularity in China, despite rising resentment of American efforts to contain the Asian country’s technology industry. The company’s iPhones are among the nation’s bestsellers and are common in both the government and private sector.

But the blockade on the devices coincides with stepped-up efforts to develop domestic technology that can match or even surpass American innovation. Last week, the release of a Huawei Technologies Co. smartphone that contained an advanced made-in-China processor caused a stir on both sides of the Pacific. State media celebrated an early triumph against harsh US sanctions, while one US lawmaker called for an investigation into possible violations of those curbs.

Foreign devices have long been discouraged in sensitive agencies, particularly as Beijing escalated a campaign in recent years to reduce a reliance on technology from the US, China’s geopolitical rival.

Employees at “some” central government regulators received instructions via chat groups and in meetings to stop bringing such gadgets into the office, the Journal reported earlier, citing people familiar with the matter. It’s not clear how widely the orders were issued, it said.

Read More: China Orders Government, State Firms to Dump Foreign PCs

In 2022, Beijing ordered central government agencies and state-backed corporations to replace foreign-branded personal computers with domestic alternatives within two years, marking one of the most aggressive efforts to eradicate key overseas technology from within its most sensitive organs.

The Biden administration, meanwhile, has sought to limit exports of cutting-edge semiconductor equipment to China. And China’s top chipmaker, Semiconductor Manufacturing International Corp., has come under scrutiny for supplying components to Huawei — a company the US has blacklisted. 

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Even with US-China ties fraying, Apple remains highly dependent on the Asian country — both as a manufacturing partner and a market for its products. Chief Executive Officer Tim Cook celebrated that relationship during a trip to China earlier this year, calling it “symbiotic.”

China also was one of the highlights of Apple’s results last quarter, helping offset a generally sluggish period. The company is preparing to unveil its latest iPhones next week, setting the stage for a holiday quarter that is invariably its biggest sales period of the year. 

--With assistance from Mark Gurman, Jing Zhao and Jessica Sui.

(Updates share reaction in the seventh paragraph.)

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