BEIJING (AP) — An outspoken college law professor calling for constitutional rule has been banned from teaching, as the Chinese authorities tighten ideological controls, including launching an unusual assault on advocacy of constitutionalism.

Zhang Xuezhong, a teacher at East China University of Political Science and Law in Shanghai, said he was notified last week that he is no longer qualified to teach any course at the school.

University president He Qinhua declined to comment, and calls to the university’s news office were not answered on Saturday.

Zhang said university officials said his June article critical of anti-constitutionalism was, in fact, unconstitutional and in violation of laws regulating teachers’ behaviors.

China has a constitution, but it is secondary to the Communist Party, while advocates of constitutionalism want the party to operate within the constitution.

A weekly newspaper in southern China was heavily censored earlier this year when it suggested China’s dream should be the dream of constitutional rule. Since May, state media and party publications have published a series of strongly worded editorials denouncing talk of constitutional rule, saying it was a western political tool that is incompatible with China’s social system.

In his June article, Zhang warned that the editorials would stifle the propagation of constitutional values such as freedom of speech, democracy and rule of law, and urged China’s leaders to build a constitutional nation.

Zhang has a history of irking the authorities. He is a staunch opponent to China’s political indoctrination of its youth, arguing university students should be spared from the compulsory, ideologically charged courses on Marxism.