Topic: Employment letter wording

Hello, I have a GC interview at the US embassy next month but my employer is not willing to sign an employment letter with the wording of " hiring on a permanent basis" or something to that effect and has only given me a letter stating my current position, salary, and job discripton. Is this lack of " permanent basis employment" wording material for my application to come through? Has anyone here obtained their green cards with a generic employment letter? Thanks a lot in advance!