PLEASE REPLY: URGENT: H1B Amendment - Change of Client and location

Hello,

My previous project ended and my next project is with a new client at a new location. Does my employer need to file H1B amendment or just LCA is enough? Is there any possibility of LCA or H1B Amendment rejection? When can I start working with new client at new location, is it only after approval? What are the timelines I can expect for approval?

Thanks.

Bashwin