The activists and 15 others -- including women and children -- were arrested in early September at the end of Ramadan.
The other 15 have been freed, but journalist Alirza Sarrafi, teacher Mehdi Naimi, poet/journalist Said Mughanli, and writer Hassan Rashidi are still imprisoned. It is not clear what crimes they are being accused of.
The Association for the Defense of Azerbaijani Political Prisoners reports that the hunger strike began on October 25.
Sarrafi, Mughanli, Naimi, and Rashidi are well-known advocates for cultural rights of ethnic Azeris in Iran, including right to native language education.