Time restrictions on H1B transfer?

Do I need to work for my current employer for a certain period (like 6 months or longer) before I can transfer H1B to another company? Thanks.

I asked the same question before:
http://web.wenxuecity.com/BBSView.php?SubID=immigration&MsgID=171378

Somebody kindly mentions "The lastest INS memo says yes". However, I can not find the memo. Where can I get the memo's weblink or other information source? Thanks again.