China is tightening the screws on internet access, again. The latest crackdown—an evolving effort to ban virtual private networks (VPNs) not under government control—could seriously erode scientists' ability to stay connected with peers abroad.

"Internet accessibility is a major obstacle for our research. It makes international collaboration difficult and damages the reputation and competitiveness of Chinese science institutes," says an astronomer in Beijing who, like others contacted for this story, feared possible repercussions for criticizing official policy and asked to remain anonymous.

China's Great Firewall routes virtually all incoming international internet traffic through a handful of access points, where government servers block access to blacklisted domain names and internet protocol addresses. The list of forbidden sites—Wikipedia tallies at least 3000—includes social media platforms such as Facebook, YouTube, and Twitter. China reportedly has 50,000 internet police who monitor domestic social media sites, deleting posts deemed seditious or merely critical of the government. Sites now commonly used for research are also blocked. These include Google Scholar, important for scholarly searches; Google Docs and Dropbox, which allow scientists to share materials for organizing conferences and managing collaborations; and even, unfathomably, the NASA Jet Propulsion Laboratory.

Many scientists in China routinely bypass the Great Firewall using VPN software that routes traffic through foreign servers. The central government had long tolerated VPNs, but these are now in the crosshairs.

Earlier this year, the Ministry of Industry and Information Technology announced that it would tighten regulations over internet services. That threat got real when one of China's popular services, GreenVPN, told customers it had been ordered to cease operations by 1 July. Then, on 10 July, Bloomberg News reported that the ministry had instructed telecommunications carriers to block VPN access by all individuals in China by February 2018. (An online Chinese news site later claimed the ban would only apply to those who don't have a license to use a VPN; it did not say who might qualify for a license.) Shortly thereafter, Apple pulled many major VPNs from its China App Store, and other online app and software sites followed suit.

Internet access "has definitely gotten worse," says a geneticist who splits his time between institutions in China and overseas. The new restrictions make working in China "a total disaster," he says. And they are likely to be a shock for both foreign and Chinese scientists working overseas who might apply for positions in China. The astronomer who spoke to Science recalls instances in which applicants suddenly couldn't access materials needed for presentations. "This affects their performance and discourages future applicants through word of mouth," he says.

Even before the crackdown, scientists had to cope with slow internet speeds. With an average connection speed of 7.6 megabits per second (Mbps), China ranks 74th globally, according to a recent study by Akamai Technologies of Cambridge, Massachusetts. That is less than a third as fast as South Korea, the world leader at 28.6 Mbps.

An unusual proposal last March from Luo Fuhe, vice chairman of the China Association for Promoting Democracy, a minor political party, declared that slow internet speeds and restrictions on nonpolitical sites were having "an enormous impact on China's social and economic development, and on scientific research," according to China Digital Times, a California-based website that features uncensored news from China. Luo proposed boosting bandwidth and relaxing restrictions on access to websites frequently visited by scholars. Most news of Luo's proposal was quickly scrubbed from Chinese websites, according to China Digital Times, but a source involved in drafting Luo's proposal said it is now "being reviewed" by Chinese authorities.

Luo's proposal came in the wake of a similar plea last year by 78 Chinese academicians in a letter to President Xi Jinping. Internet restrictions are "a great burden for those engaged in scientific research," the letter stated, according to a post by Cai Shen Kun, a popular blogger, on the opinion-sharing site 360doc. Science was unable to obtain a copy of the letter or determine whether the government had responded to the academicians.

China's internet restrictions wax and wane, often with key political events. Some observers believe the current squeeze might be relaxed after the 19th National Congress of the Communist Party of China, scheduled for November. Held every 5 years, the congress often showcases orchestrated transitions in leadership posts. Internet restrictions help keep critiques out of the public eye.

In the meantime, researchers are looking for alternatives to foreign sites. Baidu Research and Bing Research—homegrown Google Scholar rivals—have improved, says a university-based information scientist. The gap with Google Scholar, he says, "is getting small." And an unofficial Google Scholar mirror site is accessible within China.

The geneticist says he intends to use government-approved VPNs, which may be the only ones working in February. "I have absolutely no qualms," he says, even if that allows the government to monitor his computer activity. "So what? They already do," he says. What grates on the Beijing-based astronomer is the hazy policy. "The most damaging part," he says, "is the nontransparent and uncertain nature of the filtering."