TikTok parent ByteDance is asking Chinese employees at its Singapore headquarters to pay tax to their home country or risk losing their ability to cash out on stock options, as Beijing steps up enforcement of its global tax scheme.

Employees at ByteDance who relocated from China to Singapore received an internal memo on Tuesday requiring them to report their income to Chinese tax authorities and pay relevant taxes to cash out on stock options that make up a significant portion of their pay, according to three people with knowledge of the matter.

Those hired locally with Chinese citizenship were encouraged to report their income but not required to do so, according to the people. More than 1,000 employees could be affected, and the tax difference could be as high as 21 percentage points depending on individual salaries, as both countries have a tiered tax structure.