Govt.servent joining ngo

Can join if the organizational objectives conform to to public interest and not detrimental to the Government polices.

check central civil service( conduct) rules 1964  15(2) 

Any government servants can join an NGO but no amount will be taken as honorarium. 

Hello, Greetings of the day!
For the query you posted, I would suggest that:
Yes, you can join any NGO but it should be for the welfare of the people and not against the government policies. Also, government employees can’t just join to get the honorarium. You should not just generate any income through that. Even if your NGO has a nature of generating income you should not use it for your personal needs i.e., you should not depend on it for your requirements. If you have all transactions clear and transparent then you can definitely free to join any government service.
For Better Guidance, please consult a lawyer.
Hope it helps
Regards,
Sneha Jaiswal

Law Student