In practice, the centers are internment camps in which as many as 1 million minority Muslims have been placed in the past 12 months, according to rights groups and NGO reports.
The amended legislation states that Chinese regional governments "can set up vocational education and training centers ... to educate and transform those who have been influenced by extremism."
However, besides teaching the Mandarin language and providing vocational skills, the centers are now directed to provide "ideological education, psychological rehabilitation and behavior correction" under the new clause.
Beijing denies that the centers serve as internment camps but has admitted that even petty criminals have been sent to such centers. Former detainees have told rights groups that they were forced to denounce Islam and made to profess their loyalty to the Chinese Communist Party.
"It's a retrospective justification for the mass detainment of Uighurs, Kazakhs and other Muslim minorities in Xinjiang," James Leibold, a scholar of Chinese ethnic policies at Melbourne's La Trobe University, told the AP news agency. "It's a new form of re-education that's unprecedented and doesn't really have a legal basis, and I see them scrambling to try to create a legal basis for this policy."
Members of the Uighur, Kazakh and other Muslim minorities who live abroad have indicated they have been unable to contact their relatives in China.
The Chinese government has for decades tried to suppress pro-independence movements among Xinjiang's Muslim community, spurred largely by frustration over the influx of migrants from China's Han majority.
Chinese authorities say that extremists in the region have ties to terror groups, but have given little evidence to support that claim.
The latest legislation comes after the regional government launched a crackdown on halal products and banned the wearing of veils.
Read more: China state media justify Muslim Uighur crackdown to prevent 'China's Syria'
China faces international condemnation over campsFollowing the Xinjiang region's law change, a bipartisan group of US lawmakers proposed legislation on Wednesday urging President Donald Trump to condemn the "gross violations" of human rights in the northwestern Chinese region.
The proposal put forward by the Congressional-Executive Commission on China calls on Trump to press his Chinese counterpart, Xi Jinping, to immediately shut down what it described as "political re-education camps."
It also proposes imposing sanctions against Xinjiang's Communist Party chief Chen Quanguo under the Magnitsky Act, which would prevent him from entering the US and freeze any assets he has in US banks.
Read more: China's Xinjiang Muslims 'require DNA samples' for travel documents
"China's authoritarianism at home directly threatens our freedoms as well as our most deeply held values and national interests," Florida Senator Marco Rubio and New Jersey Representative Chris Smith, both Republicans, said in a joint statement.
The European Union's top foreign policy official, Federica Mogherini, expressed similar concerns last week.
The measures proposed by US lawmakers come as tensions between Washington and Beijing continue to escalate over tariff disputes and American complaints about China's technology policy.
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dm/rc (AP, AFP, dpa)