h1b approved,no client,no stamping, employer asking for money

hi i got h1b approved through comany A in 2013 even without a client. my employer not getting a client till now, so i couldnt go for stamping. but now my employer is asking for a huge sum saying that i should incur expenses if i dont join them with in few weeks from now. i signed and sent offer letter before applying the petition last year. nothing was mentioned in the offer letter about if i dont join.

please advice me on how to handle this.

If your emloyer is able to provide you client, why he wanted you to join?

my employer still dont have a client for me but he want me to try for stamping. otherwise he want me to sign a document which mention that i sud agree to pay a huge sum if i can join them in few weeks. not sure if he could revoke my approval. As i dont have a visa yet will i be able to transfer if my employer revoke? also will it cause any legal problems for me? it will be helpful if someone answer my doubts.

thank u for clarification.