After just eight months on the job, João Ribas has stepped down from his post as artistic director of the Serralves Museum of Contemporary Art in Porto, Portugal, in response to the museum’s censorship of a Robert Mapplethorpe exhibition he initiated.

The curator told the Portuguese daily newspaper Público that he was “no longer able to continue to lead the institution” after it had removed 20 works from the show “Robert Mapplethorpe: Pictures” and restricted access to certain parts of the exhibition for visitors aged 18 and under.

When the show opened on Thursday it contained only 159 of the 179 photos Ribas selected from the photographer’s series of New York’s S&M scene in the 1970s. And although Ribas agreed to warn visitors of the explicit nature of the photographs at the exhibition’s entrance, he did not consent to excluding young visitors, telling Público “a museum cannot condition, separate, or delist access to works, to say what people can see or not.”

Soon after news of Ribas’s exit surfaced, an open letter addressed to Ana Pinho, president of the Serralves Foundation, appeared online denouncing the museum’s decision “to succumb to moral puritanism and social conservatism” at a time when “right-wing populism, ultranationalism, and threats to artistic and academic freedoms” are at an all-time high.

The letter was signed by art-world luminaries including artists Wolfgang Tillmans and Tania Bruguera, as well as curators Stuart Comer and Pablo Leon de la Barra.

In response, the Serralves Foundation issued a statement to Spanish newspaper El País denying that it censored Ribas’s show and insisting that all the works on view were chosen by the curator. “From the beginning the proposal of the exhibition was to present the works of an explicit sexual nature in an area with restricted access,” the statement read. “Serralves is an institution visited annually by almost a million people of all backgrounds, ages, and nationalities, including thousands of children and hundreds of schools, the foundation considered that the visiting public should be alerted, in accordance with the legislation in force.”

“Invoking the Portuguese law on the classification of ‘pornographic’ material to restrict access to some sections of the exhibition is disingenuous and insulting, considering the vast number of erotic and/or sexually-explicit artworks that have become part of the Western Art Historical canon, many of which have been previously displayed in your Museum without equal enforcement of age restrictions,” the letter said.

A statement from the Mapplethorpe Foundation published by ARTnews seemed to support the museum’s version of events. “We do not believe that any censorship occurred,” the foundation told the site. “The restrictive signs posted outside the two smaller galleries reflect the decision of the board of the Serralves,” adding that it doesn’t dictate how institutions choose to present the photographer’s work. “We try not to interfere with any curatorial decisions nor with any museum’s internal issues.”