I read in the news (mirror):
[Facebook] would take a more “measured approach” with existing employees based on job function and past performance, he said, and set a January 1, 2021 deadline for staff to update the company on their new locations for tax purposes.
Similarly, I read on CNBC (mirror):
“We’ll adjust salary to your location at that point,” said Zuckerberg, citing that this is necessary for taxes and accounting. “There’ll be severe ramifications for people who are not honest about this.”
Why does a US company need to know the location of their employees for tax purposes?