The draft law, set to be passed by the National People's Congress, would formalise policies to promote Mandarin as the "national common language" in education, official business and public places.

China's government has been accused for decades of pursuing policies to force assimilation across the vast country into the Han majority.

Social cohesion is a key focus of the new "ethnic unity" law, which criminalises engaging in "violent terrorist activities, ethnic separatist activities, or religious extremist activities".

The proposed law says it aims to "strengthen cohesion" within China, which the legislation argues is undergoing unprecedented social change.

China officially recognises 55 official ethnic minorities within its borders that speak hundreds of languages and dialects.

Government policies have already directed that Mandarin Chinese be used as the language of instruction in some areas with large minority populations, such as Tibet and Inner Mongolia.

Yalkun Uluyol, a China researcher at Human Rights Watch, described the new legislation as a "significant departure" from a Deng Xiaoping-era policy that guaranteed the right of minorities to use their own languages.

Educational institutions will now need to use Mandarin as the principal teaching language. Teenagers will now be required to have "a basic grasp" of Mandarin upon completing compulsory education.

No minority languages are specifically cited in the new law, although it will likely affect Uyghur, Mongolian and Tibetan speakers.

"It is no coincidence that the law targets spaces where children are most likely to encounter their mother tongue," Erika Nguyen from PEN America told AFP.

"The intent being to sever children's ties with their identity, history, and culture."

A recent report by PEN and the Southern Mongolian Human Rights Information Center (SMHRIC) said that more than 80 percent of Mongolian language websites in China have been "censored or banned".

Requiring fluency in Mandarin in public life could also inhibit the chances of Mongolian-speakers advancing professionally, SMHRIC director Enghebatu Togochog said in a statement.

"Economically, it marginalises Mongolians, as Chinese fluency becomes a gatekeeper for jobs and advancement," Togochog said.

The law also states that its provisions can also be applied outside China's borders.

While it calls for "strengthening ties" with overseas Chinese communities, it also warns that people outside China who "engage in activities that undermine ethnic unity" or inciting "ethnic separatism" will be held legally liable.