The UCCA Ullens Center for Contemporary Art in Beijing was forced to cancel an exhibition of Chinese American artist Hung Liu that was scheduled to open on December 6 after the city’s censors refused to issue the import permits for the works. According to the New York Times, after months of discussions with the local authorities, the center’s director, Philip Tinari, was only informed this month that the show could not proceed. The abrupt decision to shut down the exhibition comes amid mounting tensions between the United States and China.

“Topics that were once relatively open for discussion are now increasingly scrutinized,” Tinari wrote in a letter announcing the show’s cancelation to lenders. “An exhibition that might have been greenlighted a few years ago—such as this one—must now be canceled.” While the artist does create politically charged works, the pieces that were chosen for the show engaged more with culture, gender, and history than contemporary politics.

Among the nine works that the censors took issue with were a self-portrait of the artist carrying a rifle when China’s Cultural Revolution ended and a work featuring twelve schoolgirls wearing gas masks, which was based on a historic photograph taken of a school drill during World War II. Liu had originally agreed to remove the artworks from the exhibition, but the authorities ultimately decided to refuse the permits for the remaining pieces.

The incident is one of several recent examples of how China may be cracking down on culture. The new Pompidou Center in Shanghai, which opened on November 8, was forbidden from presenting four works, although it was allowed to mount the rest of the show. This summer a screening of the patriotic movie The Eight Hundred, on the Japanese invasion of China in 1937, was canceled, and last year several artworks that grappled with the social and ethical implications of advances in technology and artificial intelligence were pulled from the Guangzhou Triennial.