Google’s (GOOGL) email service, Gmail, is currently unavailable in China. The outage is widely believed to be a result of the Chinese government attempting to curb the company’s growing presence.

Reports of Gmail not working in China began on Friday and data from Google’s real-time traffic report shows a steep drop that coincides. Google spokesman Taj Meadows has said “there’s nothing wrong on our end,” and China’s State Internet Information Office has yet to respond.

“Gmail has never been openly permitted in China but there’s been this workaround. People in China have been able to use these third-party providers to access Gmail while in the country,” explains Yahoo Finance senior columnist Michael Santoli.

Chinese Gmail users would access the site through protocols like IMAP and SMTP but found that they no longer worked on Friday. “All of a sudden Gmail traffic goes to zero so presumably everyone who looks at these things says that China obviously put up a new wall that’s actually working.” Call it the great firewall.

This wouldn’t be the first case of an unexplained internet blockage by the Chinese government—YouTube, Facebook (FB), Twitter (TWTR) and The New York Times are just some of the websites that have experienced bans of their own.

The Gmail ban, however, is hurting companies in China that rely on the mail service. “A lot of companies that do business in China that are multinationals do use the Gmail platform and so it’s obviously another headache and hurdle to doing business in China,” says Santoli.

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Santoli sees this as a minor setback for Google in the short-term and a reminder that “Google does not actually have this global running room to grow. China is not a significant market for Google…it’s shocking because this is a massive $400 billion company.”

Google has had a particularly rough go in the Chinese market—since June (the 25^th anniversary of Tiananmen Square) nearly all of its services have been upset by Beijing. Google Search, Maps, Docs, Drive and + are just some of the company’s sites that are blocked. China previously asked Google to censor its search results but the company refused to comply, instead search engines like Baidu are used.

“Governments feel like they can control the flow of information,” says Santoli. “And this government is better at it than most.”

China has been accused of creating an unwelcome climate for U.S. business in general. A recent survey by the American Chamber of Commerce in China showed that 60% of companies surveyed felt less welcome in China than before and 49% believed that foreign firms were being singled out for attack. Antitrust investigations by the Chinese government this year have levied fines against both Microsoft (MSFT) and Qualcomm (QCOM).