Forcing to resign or fired after maternity leave re-joined

Dear sir, i have rejoined office after 12 weeks of maternity leave.I requested for extension of maternity leave without pay before joining the office but my request was rejected verbally by boss & HR. Due to personal reasons this job is important for me. I have a baby of 4 months now due to which I cant change my job. I am a project coordinator & look after construction projects. But my boss is forcing me to resign & threatening me to do fired from service after my rejoining. .Discrimination started since i was 9 month pregnant, boss had given a transfer letter to me.I requested our HR to stop my transfer on humanitarian ground in 9 month pregnancy, then HR accepted my request & stopped my transfer till I joined back office post delivery. Now they are not transferring me to other place & transfer letter taken back from me. After a week now my boss again saying he has given my name to HR to transfer me to other department. He is pushing me to change my nature of work. in my office there is only one project department. He told me that he has sacked me from my job & told me to talk to HR if there is some vacancy in other department, if no vacancy then you will be fired. I want to put maternity discrimination case against the company but do not have knowledge of acts & how can I appeal. I heard that employer can not fire & change the nature of work if employee joined after maternity leave. Please help me. Is there any act to save my job after maternity? is it right to put case in labor court against the pvt. ltd. company. Your valuable advice can save my job during tough time. Thanks & regards Nidhi