Indian police have arrested scores of prominent activists including communist poet Varavara Rao, human rights lawyer Vernon Gonsalves, writer and lawyer Arun Ferreira, journalist and activist Gautam Navlakha, and trade unionist Sudha Bharadwaj.
All have been charged under the Unlawful Activities Prevention Act. They are also accused of having Maoist links.
Opposition Leader and Congress party chief Rahul Gandhi has accused PM Modi's government of seeking to silence its opponents.
In a tweet message, Rahul Gandhi said "there is only place for one NGO in India and it's called the RSS, the BJP's ideological Hindu nationalist backer, Rashtriya Swayamsevak Sangh, welcome to new India".
Meanwhile, Global human rights watchdogs Amnesty International and Oxfam have condemned the arrests, urging the Indian government to respect "people's rights to freedom of expression, association and peaceful assembly instead of creating an atmosphere of fear."