Hi Stonemason
I read the end of your question as if your employer is unwilling to provide the letter can anyone compel them to do so? The answer is no - it is up to you to assemble all of the evidence you need to support your case. If you are worried about this then there will be other aspects that are likely to be a problem - after all INZ will want evidence of your employment too. They
may phone your employer as part of the verification process
I'd also expect a possible challenge from Immigration about
how your job provides
enough evidence of your English language ability. In a fabrication role like yours you can get by with very little spoken English and even less written English. So I would give some thought in advance about how you would prove that English was the "language of employment" and give examples if they ask for it - such as speaking to customers in English as well as your fellow workers, having to write things in English, perhaps procedure manuals written in English etc. Note that the following says "used in your employment" not "used by your employer" - there is a subtle difference between the two.
Assuming you are doing the work to residence route, this is what the operations manual says:
RW5.15 Evidence of employment in New Zealand
Evidence of full-time employment in New Zealand for a minimum of 12 months is original or certified copies of:
references from employers on company letterhead, which state the occupation and dates of employment and the contact phone number and address of the employer; or
an employment agreement with confirmation from the employer that the applicant is still employed.
Evidence that English was the language of employment is a written statement from the employer that English was the primary language used in that employment.
I'm not sure what you meant by "development" in your current job. In the UK we would use that word to describe training/learning activities - is that the case? Are you saying that the training was conducted in English or that you were given English lessons?