Conflict in company

Hello, I am working in a company size of around 1000 employees in India. I am 4 months pregnant and have shared the news with my manager in February. It is a high risk pregnancy and doctor has advised me to change my shift. I am working with this company for more than 3 years and since my joining I work in night shift. I requested my manager to change my night shift to day shit in February and since from that time I am following up for the solution. We have a team of 14 employees and it is divided in to 3 shift - morning, afternoon and night shift. I know it is not a hard decision for him to change the shift but still he shows to me that he trying but because of one guy who is getting married in August asked for a day shift first, he has to give him first being in que first. I warned him that I will resign if not given afternoon shift and will mention it that it was a forceful resignation. Can you please let me know if there is any law as such which should abide a company to provide a day shift to a pregnant woman first if there is an availability. P.S - I have been undoubtedly an extreme performer for this company.