Believers in Telangana state face attack from Hindu nationalists, which International Christian Concern says is often going unpunished by police.
A number of Christians have been hospitalised because of the attacks in recent months, the charity said.
At least 25 incidents of serious persecution have been reported in Telangana in the recent past although the real figure is thought to be much higher.
International Christian Concern says a recent outbreak of violence has left locals in fear and anxiety.
In August eight members of the Brethren Church were attacked leaving them bleeding in the street.
"We were beaten up in such a way that no blood or injury was seen outside," Pastor David, the leader of the group that was attacked, told ICC.
"We were tortured for more than three hours without a break, and they made sure that we don't faint and die by giving water to drink time to time in between. I thought that was the last day of our lives."
"We couldn't bear the pain and the physical harassment, knowing that there was no way out," said Mr. Narsinga Rao, one of the eight Christians. "They applied the red powder on our forehead."
The red powder was used to mark the men's "conversion" to Hinduism. If they did not comply, the extremists promised to kill them.