Jagtar Singh Johal, from Dumbarton, West Dunbartonshire, was detained in Jalandhar in the state of Punjab on November 4.
The Sikh Federation UK said no official charges have yet appeared, but local media reported Mr Johal’s arrest was linked to the killing of Hindu leaders in Punjab.
Mr Johal, who got married in India in October, has told lawyers he has been tortured with “body separation techniques and electrocution to body parts”.
The federation said up to 1,000 people will protest outside the FCO building on Friday, calling for Mr Johal to be given more consular assistance.
They will also ask for Mr Johnson to meet with the family and “make representations to his Indian counterpart demanding his immediate release and return to the UK”.
Speaking about the case previously, an FCO spokesman said: “We are in contact with the family of a British man who has been detained in India. Our staff have requested consular access from the Indian authorities so we can be assured of his welfare.