An influential Communist Party website called for him to be punished under Chinese law, despite the fact that Mr. Rehage lives in Hamburg. Coupled with events like the recent disappearances of five people connected to a Hong Kong publisher of books critical of Beijing, the episode has raised questions about China’s reach across borders.

The website, Communist Youth Net, which is owned by the Communist Youth League, published three commentaries accusing Mr. Rehage of “blaspheming” the founding leader of the People’s Republic, who died in 1976. Such people should be “shown the bright sword,” one read.

Mr. Rehage’s statement was “subjective,” meaning incorrect, and is therefore not protected speech, Zhu Wei, the deputy director of the Communications Law Center at the China University of Political Science and Law, was quoted as saying in one of the articles.

The party’s own verdict in 1981 that Mao, under whose political campaigns millions died, did more good than harm, was “objective,” meaning correct, Mr. Zhu said.