Shares of Apple fell by 2.9% on Thursday following reports that China plans to expand a ban on the use of iPhones to government-backed agencies and companies.

The world’s most valuable company is worried about its ability to do business in the world’s second-largest economy.

The stock of Apple (AAPL) fell the most in over a month on Wednesday. Currently, the Dow Jones Industrial Average’s worst performer is the company, which lost about $200 billion in two days.

It may be a sign of things to come for Apple if these bans continue.

Chinese sales accounted for about a fifth of the company’s total revenue last year, making it the company’s largest foreign market. Despite Apple’s refusal to disclose iPhone sales by country, analysts at TechInsights estimate there were more iPhone sales in China last quarter than in the United States. Additionally, Apple manufactures most of its iPhones in Chinese factories.

According to Wednesday’s Wall Street Journal, China has banned the use of iPhones for central government officials, and managers have informed staff via chat groups and meetings.

Bloomberg reported Thursday that those bans had been extended to state-backed companies, including PetroChina, which employs millions of workers and controls vast swathes of the Chinese economy.