The huge and growing population of China-born professionals in the United States is prompting many major U.S. companies to ask their employees not to travel to China.

“We are restricting business travel to and from China until further notice and encouraging our employees to follow the health and safety guidelines provided by international health agencies,” an Amazon employee told Business Insider.

“Amazon is also telling employees who have recently traveled to areas in China affected by the virus to work from home for two weeks and, if they experience symptoms, to seek medical attention before coming back into the office,” Business Insider reported.

“Facebook suspended non-essential travel to mainland China and told employees who had traveled there to work from home,” the New York Times reported.

Many Chinese migrants work in elite technology companies, not in the myriad lower-tier software sweatshops around the United States. Many others work in banks and financial-sector companies, so several U.S. financial-services companies are curbing employee travel to China.

Understandably, companies do not want to talk about their employees — and especially their number of Chinese-born employees. But the workforce numbers can be estimated from government data — and those numbers suggest Amazon and Microsoft each employ more than 6,000 Chinese graduates with relatives in China.

The website, MyVisaJobs.com, uses federal data to track job opportunities for foreign graduates in the United States.

The data shows that employers nationwide nominated 11,153 Chinese-born migrants for green cards in 2019, 12,612 in 2018, 8,603 in 2017, and 7,217 in 15. Overall, or 59,870 Chinese has been nominated for green cards since 2010 by U.S. employers. Nearly all of those requests are approved by the government, after a short delay.

The MyVisaJobs data shows that Amazon and its various affiliates have nominated 2,736 Chinese employees for green cards since 2013. Not all those nominated were approved — but the companies still employed those workers.

Amazon also hired many H-1B workers from China.

The MyVisaJobs site tracks Amazon’s requests to get to H-1B visas for almost 4,000 new foreign hires in the last three years — but it does not provide the nationalities. The federal government likey approved 1,500 of the 4,000 visa requests.

The company also sought to extend or modify H-1B visas for roughly 13,000 other H-1B workers during the last three years. The Department of Homeland Security would likely have approved nearly all of the requests, but it does not reveal their nationalities.

But one-third of Amazon’s green-cards nominations go to Chinese workers, so a cautious estimate would say that one-quarter of Amazon’s H-1B visa-workers are Chinese. If that estimate is correct, then Amazon employs roughly 5,000 Chinese-born H-1B visa workers.

To minimize possible double-counting with the green card nominees, that 5,000 number should be reduced to 4,000. If one-quarter of those Chinese green card immigrants have left the company, then 3,000 are still at Amazon.

The federal government also allows companies to hire foreign graduates who get work permits via the Occupational Practical Training program.

In 2019, the federal government reported 478,732 Chinese students in the United States.

In 2018, 25,843 Chinese graduates got work-permits via the ‘STEM’ side of the Optional Training Program, alongside 70,521 Indians and 17,000 graduates from other countries. That means Chinese provide a little more than a fifth, or 22 percent, of the overall STEM-OPT population — many of whom are invited by friendly managers into good jobs at prestigious companies.

In 2018, Amazon employed 2,911 STEM-OPT graduates, suggesting a Chinese population of roughly 600 graduates.

Amazon also hired 851 graduates with ordinary OPT work-permits and 691 foreign students with “Curricular Practical Training” work permits. The numbers may add another 300 Chinese employees to Amazon’s ranks because Chinese students comprise almost one-third of all foreign graduates and students.

So a back-of-the-envelope estimate suggests Amazon employs 2,500 Chinese-born people who have been nominated for green cards, 3,000 Chinese visa-workers with H-1Bs visas, and roughly 900 Chinese-born graduates with STEM-OPT, OPT, or CPT work-permits.

That population adds up to 6,400 Chinese-born employees — nearly all of whom have parents and relatives back in China.

Microsoft also has many Chinese-born employees in the United States.

Microsoft has nominated roughly 3,400 Chinese citizens for green cards since 2010. In 2018, it employed 690 STEM-OPT graduates, 243 OPT workers, and 580 CPT workers. The company asked for 394 new H-1B workers in 2019, 1,509 in 2018, and 1,515 in 2017. It sought another 10,400 H-1B visa extensions and modifications since 2017.

Once adjusted by the same low ball fractions as in the Amazon calculation, the federal data suggests Microsoft employs at least 6,000 Chinese-born employees.

“Based on the evaluation of risk communicated by global health authorities we have advised employees in China to work from home and cancel all non-essential business travel,” a Microsoft employee told Forbes.

“We place tremendous value and focus on the well-being and safety of our employees,” Amazon told Business Insider. “Out of an abundance of caution, we are … encouraging our employees to follow the health and safety guidelines provided by international health agencies such as the CDC and WHO.”