ARNIKEFI

I have just had my H1B application accepted and should be heading for the US at the end of the month.
The problem I have is that my prospective employer is trying to change my salary - and not for the better!
Does anybody know how long I have to work for him before I can transfer the H1B?
There are two other companies in the US that have been keen to employ me and I am now considering approaching them.
Any help on this would be greatly appreciated!

Thank You!