Cuban opposition activist Roilán Álvarez Rensoler has been on a hunger strike for 36 days and is now in serious condition, relatives said Friday, as he demands his release from detention.

Álvarez Rensoler, a member of the Patriotic Union of Cuba (UNPACU), a leading Cuban opposition organization, is being held in a detention room at Lucía Iñiguez Hospital in Holguín, according to denunciations by UNPACU leader José Daniel Ferrer.

Family members say doctors have already classified his condition as serious. His mother and sisters are demanding proof that he is alive, saying they have not had direct contact with him for several days.

According to reports from Martí Noticias, Álvarez Rensoler was arrested on January 30 along with activists Dariel Calderín Rensoler, Jorge Luis Hernández Haber, and Jordán Méndez Martínez after antigovernment posters appeared in Holguín and a billboard with Fidel Castro’s image in Birán was damaged.

The opposition activist was taken to State Security headquarters in Holguín, where he began a hunger strike demanding his immediate release.

Cuban authorities accuse him of the alleged crime of “propaganda against the constitutional order,” a charge frequently used against political opponents on the island.

Relatives say they have also faced harassment and surveillance by State Security while demanding his release.

His relatives have not stopped demanding his release and even have been repressed for it, through arbitrary detentions and surveillance.

The Cuban Observatory of Human Rights (COHR) demanded on Thursday the release of the opponent and condemned the violation of his rights.

The activist has been a political prisoner before on the island.