New Delhi, July 1 -- China's Ethnic Unity and Progress Promotion Law came into force on July 1, formalising President Xi Jinping's vision of a unified Chinese national identity. Beijing says the legislation promotes ethnic harmony and national security, but critics-including the United Nations, Taiwan and international rights groups-warn it could accelerate the assimilation of ethnic minorities and expand China's legal reach beyond its borders.

Here's what the law does and why it has become controversial.

The law aims to strengthen what Beijing calls a "shared Chinese national identity" among the country's 56 officially recognised ethnic groups.

China's Han majority accounts for more than 90% of the population, while minorities include...