I was working for Wipro and they send me to Germany for 1year,during this time i applied for my H1 Visa and got it stamped and my project in Germany also over now i put up my resignation.Now they ask me to pay an amount of 5Lakhs or i work for 6months.
There is no such bond which i signed and i do not understand on what basic they ask for this.I asked them to give me the details but they are not ready to give anything in writing and asking for an amount.I am ready to pay for the 6months Indian salary as i want to quit soon and start working in US.I can understand if a person leave the client site in the middle of a project but i finished my project and currently i am sitting idle doing nothing.
I could leave the company without working for a single day or paying any amount but they will not give me a relieving or experience letter.
How can one tackle such kind of harassments by employer.

If no such bond is signed and if you do not want to pay the amount which they have asked, you can definitely file a legal notice to Wipro - HR dept in your home country. Normally international bonds are not valid, and since you have not signed anything, so you can even demand a ransom amount to Wipro for such harrasment. Do work for certain period so that you complete a minimum notice period and then leave.

contact a lawyer specialising in Arbeitsrecht.