An explanation will be required from your employer on official company letterhead as to why an employment reference letter cannot be provided

189-190-visa
2

We have seen that ACS is rejecting the assessment if you can’t provide the letter from employer.

Here are real life case:
https://forum.am22tech.com/t/an-explanation-from-your-employer-on-official-company-letterhead/7873?u=anil.gupta